No, they will have left the Northern fleet by December so there is little point in undertaking such major work on them. Any reinstatement of the HD can be done by their next operator.
On a different note, the 14x,15x,158 & 159 brake solely using the friction air brake. If the T211r transmission has a retarder capability it certainly isn't used. I would imagine the 16x and 170 family are the same.
16X, 170s and 171s do have the same T211r transmissions as the Sprinters and Pacers, as AFAIK do the 175s. The 180s and 185s have a different transmission due to having more powerful engines.
I think the nature of the British network probably has a lot to do with why we've never gone for dynamic braking as much as other countries. A particular thing is that we've not go the same long, steep decents found in many other places where dynamic braking really provides a big benefit. The only place where it's been common has been on tramways (where rheostatic brakes have been in use since the early 20th century) and the Underground (although not until the late 60s).
It's not just railways either. Dynamic braking has been common for some time on lorries and buses in other countries, especially the likes of America. Again it's the nature of the roads, we don't have the same long steep decents, and were we do they aren't on the sorts of roads that buses and lorries would be using. Exhaust braking also has a noise issue, again not so bad on isolated mountain roads but a problem in the densely populated UK. Exhaust braking on lorries and coaches, and electromagnetic retarders on coaches and buses didn't become common in the UK until the 80s when imports from Europe became more common, including UK manufacturers importing European or American (particularly ZF and Allison) transmissions with built in retarders.
When it comes to other countries using dynamic brakes on long steep decents, it's important to remember that it's not just an issue of brake wear but a safety issue. Overheating brakes can easily cause brake failure and runaways. A heavy freight train or a large lorry that's lost it's brakes going down a steep hill is not a good thing at all, yet had happened, and even today still can happen.
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