http://www.ft86club.com/forums/showthread.php?t=40066 
280whp on 91 is unlikely, I'm using 70mm on the equivalent of your 93. I'm on roughly 250whp. Expect +10bhp for a manifold. The Sprintex runs out of efficiency at the top end so smaller pulleys gain less peak power. On non-E85 the OEM fuel system is fine.