I run a holley 750 race DP on a Victor Jr. The RPM manifold is a good intake, but will not make as much power as the Victor between 4000 and 7500 - maybe 15 to 20 less a peak. Do you know if the cam is a roller? I think it is pretty clear that you have a very mild cam in that pup (ie. no lope). My cam is a ford mortorsports M-6250-A351. It makes over 300 RWTQ at 3000 RPM. See my gallery for a pic of the dyno run.
Comp Cams tech is very good. Also, a lot of guys on this site as well as
www.corral.net are very good at picking cams. Spend some time and ask a lot of questions. Just make sure you are honest with yourself about how high you want to spin the motor. If you are not careful, you can end up with something not very streetable. My engine is the 385 HP ford crate motor with a set of AFR 185 heads. While the block is a Sportsman model, the crank and rods are not forged pieces. Hence, I shift at around 6200 on the road course. I have shifted as high as 6800 on the drag strip. Also, make sure to order the right type of cam for which your block is currently set up for: roller, non-roller hydraulic, solid etc.
I believe there is an easy 50 hp in a simple cam swap. Throw on a set of underdrive pullies ($100), put a good K&N filter on if you dont have one already and head back to the dyno. Take the time to tune the carb and play with the timing while on the dyno. Also, investigate the actual sidepipe muffler itself. Sidepipes are notorious for sucking out huge HP figures. I have heard that even some of the better pipes out there can swallow 100 HP on a big block If you have a restrictive bullet muffler in the sidepipe, there could be lots of power on the table there too.
I recently had a new set of sidepipes made that are totally tunable with excellent guts including collectors costing $250 a pop and the muffler insert costing $300 a pop. I tested these on the dyno and the difference between the low setting (quiet) versus the medium setting was 50 hp - yikes. I will post the whole sidepipe story complete with dyno figures and pics soon in the Shop Talk forum.