Need help and info to help out my autistic son with his project

I have been told that the Schumacher Tri-Y's will drop into an early A-bdy big block car. But I don't have proof of that.
Another, and very inexpensive option (people will give you a set for free and although not great for exhaust flow) is to use a set of earlier big block "log type" exhaust manifolds, and if necessary, have them AND the spot faced mounting nut flats angle milled to bring the rear dumps in closer to the block. They should fit inside the stock '63-66 factory inner fender sheet metal. These were the "common" manifolds on the big block B-bdy and C-bdy cars into at least 1966.
Hope it helps... YMMV
Mike in FL