What is the rest of your combo like? Just looking at what you have posted, I would think you are fouling the plugs so fast it wouldn't even run! So a small block running the l98 heads, your jets are way too rich... also, your squirters and primary pump are too big for a small-block. That carb would feed a very healthy big-block!
I would be willing to bet that what you are experiencing with smaller jets is not a lean mis-fire, but rather the engine loading up on fuel and sputtering.
To give you another idea, a factory Holley 750 for a big-block application comes with 70 jets in the primaries, 78 or 80 secondary jets, and .028/.031 primary/secondary squirters.
My recommendation is to find a 600cfm, or re-jet your present carb WAY down. You will probably need to be in the 64 primary jet range and 68 to 70 secondary jets.
Best of luck,
Colorado Springs, CO
68 Camaro... someday!
71 Chevelle SS