The direction you're heading is certainly one way to get a good fitting radiator that will fit within the stock dimensions while avoiding the ridiculous prices of the big name aftermarket radiators.

I was in the same boat with regard to cost but also didn't have my stock 37' radiator to re-core.

I simply bought a $170 aftermarket aluminum radiator from an AFCO distributor on Ebay. I went with the largest size that I knew would fit with my stock grill shell support. Given that these are typically crossflow radiators, I cut-off and capped-off the existing neck and mounted the radiator sideways in my grill shell support. This placed the hose inlet and outlets in the correct position as with a vertical flow radiator. Then I simply added a fill neck in the upper radiator hose between the radiator and the thermostat housing and, a petcock-drain in the lower hose. This set up cools very well on a 400 hp small block.

- EM