Well Saleen put a 351 in some of their cars in a 99+ body, but the 351 is a small block. Thats a known fit, and im sure there are all the parts you need for the swap available. IF you wanted more, you could work that engine over, make it a stroker... whatnot.
Im sure you COULD fit a big block under the hood, but it probaly takes alot more work and fab than a small block swap. Small blocks are still old school...