Badger, you are ancient. The only work I have ever done with Shermans, outside of museums, is to shoot M72 and Carl G rockets at them.
The electric firing solenoid would be a prohibited device by todays laws. You are not allowed to fire a gun by electric means in Canada. Not really sure why; I guess they figure you could make it shoot fast that way, or else they were watching too many James Bond movies.
Anyway, back to the subject backplate...if you are going to use that plate in one of the semi auto 1919A4s converted to 8mm swede, you might want to reconsider. The 8mm is a bit more powerful a cartridge. Less buffers may increase the wear on them, so you might want to inspect the discs a bit more often. I think I read on 1919com where a guy found nothing but powder in there. Of course, you will want to open up your front barrel bearing to reduce the recoil.