Why are 318's low HP and torque?

273... Do you mind running my numbers through to give me a rough estimate?

318
600 Holley vac
Performer intake
Hedman Shorties on 2.25 duals w/ x-pipe
302 heads w/ .028" head gasket (gasket matched w/ 1.88/1.60 valves)
Comp XE268 cam

also:
2000rpm stall on 904
2.94 gears (trying hard to find 3.55 SG)

(Red Line)277hp@4500rpms
(Green Line)366FT-LB@3500rpms