I have these numbers in my notes for an SBC to a stock 3100 radiator.
Gates 20416 upper
Gates 20584 lower
I put a SBC in a GMC and I used a flex hose for the upper, IIRC it's 18" long with one end being 1.5" and the other 1.75".
On the GMC radiator in my 49 the bottom connection made a 90 degree turn up so I had to find a hose that was close enough with the right sizes then cut it in half and splice in a 1.5" copper 90 elbow to get it to fit. The hose was spec'd for a 78 Jeep Chrokee w/a 4.7.
