Keeping to the context of LM 304s and 310s, where it was posted upthread about commuter shorts trains LH with AC Mk2, what contemporary trains were these refering to the LM ? I can't ever think of any. Cobblers were not short, and were mostly (all ?) Mk1.
There were short LH sets that ran with ACL - there were the three or four 5-6 car Mk2 PV (not AC) sets in the assorted Birmingham / Crewe / Preston / Lancaster / Barrow circuits - but these were not commuter trains per se they ran all day which obviously covered certain am and pm peaks in doing so.
The only short ACL LH slow/stopping 'commuter' train I can think of, at least late 70s and into 80s in west midlands, was the evening peak 17:21 SX Birmingham Euston semi slow (ecs from Oxley) that went from EMU to load 5 vac LH in about 1984 or so, and ran in the same path same timings as 310; stock returned in those timetables 00:10 ex Euston vice EBW AC set (couple of timetables before 0010 SO became the overnight Aberystwyth). It was in effect of the very early days of BR Sectorisation. There was no correspnding a.m. peak working.
310s worked to Carlisle. On a few high peak summer Saturday c.1983/84 the 'Clansman' had a Birmingham - Carlisle relief running in front of 1S53; the booked single 310 right away then ECS to Lancaster; then formed a relief in front of whatever the next southbound AC XC to/through Birmingham was (not 1M42; EMU came back erlier then that iirc). IIRC New Street crew to Preston and conducted north thereof.
I mention crewing as one of the limits setting the arbitrary approximate 310s south of Birmingham 304s north of rule of thumb was crew traction knowledge; New St / Wolverhampton / Rugby sure knew both 304 and 310, but AIUI depots north did not know 310s and depots south not know 304s; of course that did not block their use as they were simply crewed by a depot that did know the train type and knew the road anyway.
Why then was the Birmingham Carlisle EMU a 310 not a 304 ? Allegedly, and this is the reason given at the time, not some wibble from the web this century, is non gangwayed trains not permitted over Shap. I am not going into why or when or how that came about, nor even if it is correct, only saying that was the reason given to me at the time by a LMR diagrammer at Crewe. Yes I know, and had already been said upthread, 310 were not fully gangwayed*** but 2+2 so what precisely this 'rule' is was unclear.
12car LM 310 : no-one mentioned any yet. There were occasional Birmingham Euston 'adex' / 'shoppex' trains that were more often than not 12car 310; not a great quantity of these, maybe only 3-4 a year at most, and, were usually weekends, including Sundays, when enough 310s were spare. Oddly these ran with exactly the same stoping pattern as bog standard EBWs - but at a much lower fare.
IME early 1980s 23:15 Sun Birmingham Euston semi fast was regular 12car ex NewSt at least to Rugby but ISTR it detached units somewhere and was not 12car throughout.
12car 304 ; were there ever any ? NOT ECS, I mean 12car in passenger service ?
304s : these were ordered and built in 3 seperate batches - but the second two are nominally the same. 001-015 were open driving trailers and compartment both middle cars; 016-045 three opens and only the trailer composite was compartment. The batches 001-015, 016-035 and 036-045 were ordered against sucessive OLE phases. There are maybe electrical differences with the 001 batch too but I need go look that up.