I just found a PSI spring that might work better with a flat tappet cam. LS 1512 ML is a dual spring with 130lb on the seat @ 1.800" and 375lb open at 1.200" here:
1500 Series - Performance Springs
However, if you're going to rev it to 8000rpm (as stated on the cam card redline), then I'd probably use something heavier.
As always, check with the cam manufacturer first to see what spring pressures they recommend.
