looking to rebuild my 84 J10. it has 258 engine / 4spd manual trans . Motor needs work so was going to replace it has been sitting for 20+ years was wondering what engine would be suitable ? with minimal work 350 chev? 360 AMC, 5.3 chev?
The 1984 J10 was rated maximum at Class III for 5,000 lbs trailer weight. However they recommended extra duty springs, a proper "equal hitch receptacle" instead of the bumper hitch, an auto transmission with cooler and a 360 V8 was "Required" for Class III.
The J20 was longer wheel base and could tow Class V at 7500lbs or even 8000lbs with a 5th wheel.
Would you run into issues towing 6500lbs? Maybe from the smokies and maybe when your rig jacknifes. The shorter wheelbase counts against towing.
If you could get the trailer weight down to 5,000 lbs I would go for a lot more grunt, auto trans, trans cooler, heavier springs, proper hitch, 7 way trailer electrics, trailer stabiliser etc. You will need more grunt than a 258 on the hills, the 360 will do it but you can take your pick of the larger V8s, maybe even a big block.