My first pump gas stroker 511 C.I.(4.375 bore with 4.250 stroke)stock iron 400 block made 612 Hp at 5500 RPM and 544 ft lbs torque at 4500 RPM with a mild set of ported big valve 906 heads and stock type six pak intake and vacume carbs. On your deal with a aluminum block build a 4.5 bore with either a 4.25,4.375 or 4.500 stroke with BB Chevy rod journals That combination, either of the three,will make 600 HP on pump gas at 4500 RPM with a set of decent set of unported aluminum heads My 511 became a 517 C.I. by increasing the stroke to 4.300 to move the dished pistons up to zero deck to make 10.29 to 1 compression ratio, I later swapped the heads to a set of M.W. port size Indy SR (10.78 to 1 comp. ratio)and a Indy 400-3 intake witha single 1050 CFM Dominator and that combination made 728 HP at 7000 RPM in Klamath Falls Oregon at 4300 ft above sea leve Good heads on a big C.I. motor make a hoop of power On the aluminum block deal make sure to considered the block growth on the final compreesion ratio, the aluminum blocks are known to grow between .006 to .010 in hieght warmed up The aluminum block needs to have dry sleeves to work well on the street also, it will loose a little power compared to the same combination in a iron block but on a street car with stock type suspension and stock type tires you will never know the differences in that power. Be very careful in the car until you get use to that kind of power, it is additive and can be very dangerous My 3450 lb. (with a full tank, 18 gallons, of fuel) Duster went 9.993 at 134.7 MPH through the full exhaust sytem with the air cleaner on using Oregon 91 octane pump swill