What's the plan for the roundabouts? The other direction of traffic?
I like your enthusiasm, but your Stratford road narrowing idea is not feasible sadly.
No highways department would agree to running an active railway that close to a main road, let alone converting a road to timed single track one way operation.
Recently the government announced that were scrapping road building/improvement plans to fund defence and I found it interesting that no car magazines or other motoring supporters kicked up a fuss and I reckon it is because even the most petrol of petrol heads realise we can't go on building endless roads for endless traffic and that rebuilding/new heavy rail is the only way to go to move people and freight around.
The problem is that the powers that be are still keen on roads/don't want to spend upfront costs on building railways so all it takes is a road - either crossing the track bed or on it, a house, factory, warehouse or any other building foot/cycle path or any other excuse and 99% of the time it is "No" to the railway or if by some miracle its "Yes" to the railway then we usually end up with a bodge job.
For example while it is good Portishead is coming back on to the network the same mistake is being made that was made when the railways where originally being built and that is building the railway station on the outskirts of where it is purported to serve, and while it was not a major problem back then because if you did not use the train your only options were to walk or ride a horse these days the options are car or bus/coach. So what should have happened is the line should have been built all the way back to Portishead high street with a level crossing/bridge/tunnel/road closed and either the petrol station or the shop unit next door demolished for the station site.
What we need is a total mind reset and it needs to be 100% of the time "Yes" to railway's and "Tough" to whatever is in the way. So concerning Stratford, at the southern end of Seven Meadows road there is space to either build a road over bridge or a tunnel under. With the road its self, either close the road completely or put those concrete barriers you see on motorway central reservations between the road and the railway to stop someone accidentally/deliberately driving on to the tracks then top it with a high fence.
At the northern end of Seven Meadows road it would be a tight squeeze to fit a in a bridge/tunnel in, so I saw a picture somewhere a while ago where in another country they had put a heavy rail/tramline straight through the centre of a roundabout so I don't see why it cant be done here.
They aren't cranes or crane operators, which is one major expense.
You are right, it is unlikely GWSR have a qualified crane operator in their volunteer workforce let alone a big enough crane.
I am not a engineer or a builder and the following is based on the odd visit I've made to the railway, walking a small bit of the track bed between Broadway and Honeybourne and Google maps but it seems to me that virtually all the bridges on the railway are built in the same way, namely brick abutments and then steel girders for the span and then a few more bricks to hold it all in place
With the props holding up the metal spans it suggests to me that the brickwork/foundations are fine and it is the metal spans that are the problem because, say, the foundation's were collapsing then eventually you would end up with vehicles having to "climb" up the sinking foundations, "bump" up on to the lip caused buy the sinking foundations, on to the supported metal part and then "bump" down again on to the sinking foundations at the other end and that would be dangerous particularly for cyclists.
So with all the knowledge the volunteer's have gained with all the issues that they have had then I am guessing what would need to happen is: Remove the holding it together bricks, lift out the old girders, tidy up the odd brick that looks a bit dodgy, then put in new girders and put the bricks back to hold it all together, therefore I would have thought the only cost's would be for some new steel girders and a crane to lift the old ones out and the new ones in with the volunteers doing the rest.
It sounds unusual for NR to not want full ownership.
The government aren't likely to to want to "nationalise" a heritage railway with all the costs and hassle it would entail and then rebuild it to "proper railway" standard's but as I pointed out in the Go-Op thread about Minehead:
https://www.railforums.co.uk/thread...proved-by-orr-access-rights-now-lapsed.277000 page 10 post #356 onwards if they could "rent" a heritage railway for morning/evening commuter services and make a allowance that as the trains would be modern with all the safety features and the train crew would be properly trained staff then they could run at at least 40mph then it is a cheap and easy way to bring back a railway.
To all the people discussing about services to Oxford, Cowley, London etc if this was built and a way could be found to either keep one lane of the road and put two tracks down or scrap the road and put two tracks down then services to Oxford, Cowley, London etc should be looked at but if there is only room for one track then because of capacity constraints the priority should be morning/evening commuter services Winchcombe - Toddington, day services Broadway/Honeybourne then Stratford and stations to Birmingham because as I say the only way this would have any chance of ever being built is if it can show that it removes traffic coming into/passing through Stratford rather than traffic that is already going away (driving to Honeybourne to catch a train or driving all the way to Oxford, Cowley etc).