little 'ol 273

300 hp in a 273 is only 1.1 hp/ci. bobscuda67's adivce should get you close. If you do any port work to the heads it should help alot as well.

I think a Comp Cams XE262H would work well. If you want to stick with a solid cam, the smallest they offer isthe 270S.

I ran the numbers in CamQuest for the 270S

273 0.030 over

flat top pistons, zero deck, 0.040 thick head gasket

302 heads stock flow and valves (flow numbers from Shady Dell Speed Shop which I think are a bit low on the exhaust side becasue they didn't use flow tubes )

9:1 compression with 62 cc combustion chamber (302 heads vary alot but are advertized at around 63 cc)

dual plane high flow intake (e.g. RPM Air Gap) - would need to gasket match heads

500 cfm carb

small tube headers and mufflers

299 hp @ 5500 rpm
325.5 ftlb @ 4000 rpm

the trick will be getting pistons for zero deck build, replacement slugs will be further down the hole and might require more shaved of the heads to get compression up to 9:1 needed for the 270S