Pushrods being at a slight angle while not idea are not as much of a problem as you would think. I've worked on a lot of pretty serious BBC and SBC with severe pushrod angles that would scare you that don't have issues.
On another note you CAN run a stock intake on an on center . I did it when...
When my car was running 9.30's with a 3" open down pipe , no exhaust i changed it out for a 3.5" at the track. Two runs with 3" and two with the 3.5" It picked up .05 et and .5 mph in the quarter.
I installed a pistol grip Quarter stick in a GN a couple days ago. It's supposed to fit 200R4 , 4l60e , 4l80e etc. This was on a 4l80. The shifter arm that goes on the transmission is not even close to being useable. I had to weld a piece on it and redrill the hole.