Neutral safety switch

Either the "new" switch is also AFU or else the "rooster comb" in the trans is bent 'er somethin.

You don't have the harness cobbled up do ya? Shorted, burned against the headers? Get under there, unhook the linkage so you can work the arm on the trans and rig up either a test light from the battery to the center pin on the switch, or your ohmeter and check 'er out. Center pin should be grounded in park and neutral.