I do believe the gas 502 came about as a result of Mercury Marine asking GM for more HP and more TQ than they were getting from the 454, in a package that would mount, attach and connect like the 454, and retain the manifolding from the 454.
The later 8.1L production pickup truck engine wasn't, and in fact couldn't be, the 502 because of emissions issues. Bigger bore diameters increase the difficulty of getting clean emissions, partly due to surface area, partly due to crevice volume, partly due to flame propagation / travel, and partly other details.
If you're starting with an aftermarket block, it is possible to build 605 CI without resorting to the tall deck, and still have a better R/S ratio and piston crown height than the somewhat common 632 / 638. This probably isn't a concern for anyone on here, but matters for some Camaro ( and some Corvette ) swaps where the tall-deck is a serious problem if not an outright deal-breaker.
The 454, bored and stroked to 496, offers better breathing and thus more power than the 500 Cadillac, plus forged parts are cheaper for the BBC to survive the power. Aftermarket heads for even more power still favor the Chev. The Cad is great for cheap torque from the salvage yard, if you want a TH400, but the cheap torque, the dare-to-be-different aspect, and the novelty ( which wears off rather quickly ) are it's only ( and minor ) advantages.
Good luck with the GMC 702 as it's rare, huge, heavy and costly, and while it can do torque, it's never going to be about amazing HP.
The IH offerings are news to me, and I'm thankful to have something new to learn about.