Gearing questions 84 Gmc k1500

So bought this truck get driving it down the road & I feel the rear end going out, open the rear case & chunks of steel everywhere. No biggy 4.56 gears 12 bolt posi rear, well the front has a 10 bolt with 4.56 gears Is that ok to have two different axles?  Do you want to get the front and back to gears the same, whats the best gearing combo? Everyday driver? 84 Gmc ck1500, 700r4,208 transfer case any help would be appriciated. Thanks  

as long as the gears are the same it dont matter what axles you have.and gearing depends on what size tires your running.