'87 C-10 should be an 8.5" 10 bolt. Have never seen one with the 7.5 but that doesn't mean it didn't happen.
My oldest used a Summit 1105 in his the 350 in his demo derby car (don't get me started on THAT
) it had a real healthy sounding idle and the engine seemed to be very responsive. It would idle in gear with a stock converter and throttle response was right now. For a street build I'd want some stall in the converter and I don't know how it would be with power brakes. He ususally just throws it into Neutral and pops it into the gear of choice when it's time to go. It was pieced together from left overs, the shortblock was a std. bore 350 with flat tops and it had 76cc '487 heads on it with a Performer and a 500 Holley 2 bbl. If I ever do a flat tappet 350 again that I want to sound "racey" I may give it a try.