My guess is one of a few possibilities, as Cranky stated before about your initial timing... Have you replaced the springs in your distributor? Assuming that we are dealing with a Mopar electronic distributor, my opinion is to run 2 light springs. Using your vacuum advance also is not a bad thing for a street car, and you should be able to adjust it through the center of the diaphram with an 1/8"+- allen wrench. It should run good with 8-10 initial and 36 degrees total. Another thing that I have had happen, is the fuel pump rod had gotten worn beyond its hardened end and ate away in short order.
Another issue could be if the timing chain was installed a tooth off. Without hearing it run or what the throttle responce is, you open up many more possible diagnoses without having all the needed specifics, in which some can be difficult to judge without being present.
I think 67 B-body has certainly cleared the 550hp mark, but seems like it would be more strip than street. It depends what you want, if you want to lean more towards bad *** vs. more street driving, this looks like a good blueprint in my eyes.
I have more than one car, so I can truly get the best of both worlds, but the one I plan to drive the most would be my '70 Runner, which at this time has a 440 with 906 heads, Torker intake, 780 Holley, and a .509" Purple shaft with a 3.54 Dana. I plan to go a tick more street friendly with the cam and switch to a 6-pack with the next build as I want to drive the car more, and I really like the the 3.54 rear and the old school purple shaft would prefer lower gears. Opening up the headers had a HUGE affect on the low end of this thing vs. having the 2.5" full exhaust hooked up. I now have 3" exhaust with an X-pipe and it dumps ahead of the axle.
Like Cranky stated before, the original iron heads really need bowl work, and if you have good pistons at this point, and you want to get by with the smallest investment option to get you around 500hp, I would do the bowl/blend work, cleaning up the heads that you have, and don't change the size at the port openings beyond a gasket match. Then I would lose the cam that you have, bump up your intake to an Edelbrock RPM and also move up to an 800-850 carb.
I believe the cam I settled on for my '70 RR is a Crower solid, flat tappet #32309...
294/298 adv duration,
240/244 duration @ .050"
.519"/.531" lift w .022"/.024" valve lash (.497"/.507")
112 degree centerline
With the solid cam you will need adjustable rockers and I like Hughes, or the made for Mancini Racing by Harland Sharpe bushed style roller rockers. They should be inspected for internal burrs from drilled oil passages and final cleaning. I think 67 B-body had the oil thrugh solid lifters, and I believe that is a good idea and the set I bought last were from Howards Cams.
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If you want aluminum heads you will need to get different pistons as you will want about 10.5 to 1 compression with the aluminum vs. 9.5-9.7 with the iron heads for pump gas.
With Diamond flat tops and decking your block .010" you should have .041" quench with a .039" gasket (with the 6.768" factory rods) and with the 84cc Edelbrock RPM heads you will be right at 10.5 to 1 compression. I do not know the compression hieght of the Icon pistons, but I hear good things about them also and they are U.S. made.
Another note when using the factory rods, (which I would also recommend ARP bolts and then resizing them) is to be sure that there is a notch in the rod side bearing half that oils the adjacent piston wrist pin. The H beam rods just depend on being narrower and getting some splash to oil the piston pins, and I don't personally know the compatability issues with using the narrow rods without the larger radius of the newer cranks.
Pictured is a 440 that I just built for a friend. It is bored .030 with Diamond pistons, balanced steel/forged 3.75" crank, stock rods with ARP bolts, 6qt Hemi pan, Stealth heads with Comp springs, retainers and locks, (Had to machine heads to clearance pushrods), Smith Brother's custom length pushrods, Hughes roller rockers, RPM intake, Comp XE 230/236 hyd/flat tappet cam. This cam is quite noisy for a hydraulic cam and I guess it is the nature of the more aggressive ramps with less overall duration.
I think if I was to do this over, I would just get the Edelbrock heads and a bit larger solid cam, (240-248 duration @ .050" range), and if you had a few extra bucks I would use TTI headers over the Hedmans.
