pishta
I know I'm right....
Ported as opposed to manifold vacuum to distributor will kill performance (It depends on what is correct for that year) also the kickdown linkage is also a throttle pressure sneder to the trans. the farther your into it, the higher the upshifts. So a disconnected KD will cause your car to shift into 3rd before you are out of the intersection, and put alot of stress on the bands as they will apply very slowly thinking your motor is just abouve idle when it coulf be 3000 RPM. Adjustable pushrods will cost more than $100 273 rockers and wont be as good. That clatter you mentioned could have been a lifter not pumping up, itll rattle like crazy until the check ball in there finally starts to work. They can hang up when some trash gets in there. I would pull the plugs and VCs once more and manually turn the crank with a wrench and just watch the valves individually cycle. Sometimes you can feel the sticky one with no compression fighting you. Your vacuum sounds good. Check your distributor advance plate. make sure its moving when you suck on the vacuum line, and snapping back. If the block or heads weer decked, your preload (.060 ideally) on the lifters may be excessive and there is no way to fix that short of shimming the rocker shafts or just going adjustable rockers, so much easier. 7 3/8 inches is the length of a hybrid stock 273 rocker/hydro cam. I cant see anywhere where a pushrod will contact the guide holes under stock conditions, although I have pulled a few pushrods that have tracks on them. Flexing for sure. There are videos of a strobe on a valvetrain where you can see such flexing, and valve floating.
and your right the car wasn't in front of you so you had no idea really. I tried to explain what happened and was just looking for some solid advice on where to start.. I didn't expect you to Mr. Goodwrench it through the computer screen. 
