Correct me if I'm wrong but isn't your car small and light. Slant six's have a big weight problem as they were originally supposed to be aluminum blocks. Production problems made them switch to cast iron which makes them heavy but durable. I also think the 4.0 would be a better choice.
The problem with aluminum blockes is the open deck. The cylinders are floating free at the top. That lets them move around and pop head gaskets.
I've often wondered about picking one up and welding plates between the top of the cylinder and the block. A quick clean up bore and deck should have it ready to go.
Might be able to make some power after that.
