I almost hate to be a tad pedantic after all that lovely work you've done, but if that big V8 is going to breathe properly it'll need one more exhaust pipe.
It looks like a small block Chevy engine and the two centre cylinders of each bank had a siamesed exhaust port, and you can see the increased size of the centre port of original cast manifold on the engine. Most rodders fitting straight pipes to small blocks have two similar sized pipes attached to the centre port, thus ensuring the same area of exhaust pipe for each cylinder.