I don't have direct answers to the specific questions you ask, but I do have a couple of thoughts regarding the two motors.
First is that a GMC 302 is going to swap into your truck with very little modification since the configuration is the same as was used in the GMC versions of these trucks.
On the other hand, the 292 is a more recent design and likely easier and cheaper to buy parts for.
Comparing performance of modified motors is a bit more difficult and I don't feel qualified to do that...
