Heavy - yesI've always been impressed by his conversion kits. There have been a couple customers that have had issues with wobble with heavier tired rigs, but I'd still consider giving it a whirl if I wanted 4wd.
Tired - nah
If done correctly, the conversion drives exceptionally well. The frame and the motor are the only items that don’t get rebuilt or replaced during the conversion. Replacing all the shocks, springs, steering components, trans, driveshafts etc with new/ rebuilt parts make it drive like a modern truck. Mine rolls down the highway with zero issues.
I will say I’ve seen some other diy 4x4 conversions that look unsafe at any speed.