A stock hardtop version KL60 weighs 3663 lbs.
As you can see from my postings, I am a purest and do not like to modify a classic vehicle. I do know that some people install a SBC powertrain. You will have to do a bit of research to ensure a 4WD transaxle can be accommodated.
Just a side note, a vintage Datsun/Nissan is more valuable if it retains a linage to the Nissan family of powertrains. The Nissan SD33T, used in the IH Scout, may be a good compromise.
Keith