I guess you won't have to worry about blowing connections apart at high boost levels, there's only one and it sure doesn't look like it's coming apart.
And on the high cost of the 4" exhaust pieces, you only need one, a 4" 90 right through the hood. That way it's easy to see how she's running.
One question and I will admit I don't know all the ins and out of this stuff, but how are you going to get that big thing up on boost with half the original displacement? I know other things affect boost, but I would think the size of the exhaust pulses would have a huge affect on it.
I do want to say I admire your workmanship and sense of adventure. More power to you.
Jeff