I'm as usual, late to the party.
When I welded the z bar bracket in my 66 polara I had exact measurements from a 65 3 on tree polara.
When it was time to weld I chickened out and installed the engine/bellhousing and z bar. Positioned the bracket and marked the frame rail. Then removed everything and welded the bracket.
I would tip my hat to anyone who can weld the bracket in while the engine is in place. Big block that is. Not a whole lot of room. Might be doable with small block.
