[83GMCK2500]

It is quite the mutt. As you pointed out, you have an 81+ front end (hood, fenders, core support), with at least an 83+ grille. Axles swap in and out of these with ease...the Corporate 10 bolt front could be original, but it has had at least the 6-lug hubs swapped for 8-lug ones. You still have the '79 front bumper.

If your registration says it's a GMC Jimmy then it is a GMC Jimmy. Same thing is the K5 Blazer, just better looking (I'm biased, I like the three letters).

What do YOU want to do with it, is the question? You expressed concern about the axles, why? Your friend who talked about axles is a little off the mark... Your front end has two more lug studs on each side over the stock 1/2 ton axles, think of that as irrelevant. Your rear axle though, tremendous upgrade over the original 1/2 ton axle. It is much stronger, has much better brakes, and is often times the most preferred upgrade for these trucks.