Ever consider grabbing yourself a Junkyard Mark VIII engine and stripping it to do a 4V head swap, then adding a Cobra induction and cams along with a Centrifugal and going that route? Those old 4V castings even un-ported will support enough air for your requirements and between the wreckers and Ebay shouldn't kill your budget. Not to mention you could always sell off your PI heads/VT cams and springs for a healthy amount to recoup a lot of the cost.
I bought an entire '93 Mark VIII for $500.00 Canadian. As soon as I start itching for another project, you can be sure that I'll be using its 4V as my foundation.
As a matter of fact, I was checking out what ATI had to offer the other day and some of their self contained intercooled units looked pretty tempting for the money. That might be another avenue to consider.