I am just guessing, but probably so. There was no transmission option for 1983 which is significantly larger than any offered in 1980, so I doubt the doghouse would have been reshaped at all. Just saw the ears off and you'll probably be fine.1. Would the tunnel space <of my 1983 car> be the same?
I have had flexplates break on me in the past (such as when I was drag racing my turbo Caravan), so out of habit I always install a new one every time I separate my engine and transmission. This means I installed a new one when I did my swap. Does it spec out the same as the one on your 700R4? I don't know for certain. But even if it does spec out the same, I'd replace it.2. Would I need to change the flex plate? (mine is a GM 14"; 168-tooth; external balance; dual bolt pattern)
I think they're great if you're looking for a way to spend more money. I just re-used my stock one. My cam isn't aggressive enough to demand an upgraded one. YMMV.3. Any thoughts on new converters?
I would expect it to operate the transmission just fine. Heck, I'm currently using one off a FWD Grand Prix. Anything that moves the little shift lever in the correct direction and distance ought to be fine.4. I have a B&M QuickSilver Shifter -- any issues with adapting it to this electronic transmission?