flat tappet, I'd still use the mag heads, thin gaskets, if the bores look good, just hone and rering. if not, use KB167's and deck the block to 0 deck. if you use the stock pistons, mill the heads ~.030" or so, should drop the combustion chambers to about 60cc.

springs on the mag, I'd use either gm 3100 springs and retainers, or 2.2 retainers and hughes 1110.

for a cam, I'd use a lunati voodoo 60401 with your car's weight and gearing. with the GM springs, you get about .020" less coil bind clearance, so a comp 260H would be a good cam choice.