That helps and further makes me want to go the 292 route. I've already seen a couple '68-'72 pickups with the 292 for sale for under $500 for the entire rig which I'd just swap out the 292 to rebuild and drop my SB350 into the pickup.
Conway,
I'm not an expert on Rear Axel Codes, but I believe we can safely say the "C15" designates a 15,000 Rear Axel.
By the way, with a 19,500 GVW, the 292 would be plenty good enough. The Brownie will only make it better.
You won't be the fastest from a stop, but you should be well satisfied with the performance. If you do put one in, don't forget to super tune it and let it breathe.
Bill