Can I mount a 93 tbi intake on a 99 vortec block
No, the vortec only has 4 bolts on each side, total of 8 bolts. That is if it has the vortec heads. You can bolt the older heads on the vortec block to accept your older intake. If you are doing what I think your doing, I just built a vortec motor for my 1995 Chevy Silverado witch did not have a vortec motor. I purchase a new intake manifold which would accept my original TBI, of course I purchased a new Holley TBI that accepted my original plugins since the motor ended up at about 400 hp.