EZ convertor question-balance

I am getting pretty close it looks like to starting on my car.....finally!

I have a 76 440 with a matching transmission. When I buy a convertor I can just buy an off the shelf version, not one requiring a special flexplate, correct?

I may do a 318 thing, still deciding.

Can I fairly freely interchange convertors between my early 70's to late 80's 318's?

I'm just talking about balance, not lock-up and non-lock up etc. I am aware of the 360 with balance.

Thanks so much, ROB