It's all about caliper clearance. What's the backspacing comparing the old and new, what about rim diameter...doubt they're the same. Should have come with 16" rims, so what are the new one's?
I just ordered rims for my '79 Dana 44 through 4WheelParts, and they said anything less than a 16" rim will pretty much not fit....can be done depending on your backspacing, but kinda case dependant.
If it's close, you can grind down the outer surface of the caliper for clearance, but you can take too much off if you're not careful. I got 16.5" rims thinking I might rock some H1 rims in the future and I have no issues.
Good luck