I was seriously considering a 4.3L Chev V6 for my '88 Ranger project truck. I was basically searching for the right donor vehicle when I came across an '87 Turbo Coupe and instead decided to go with a 2.3L turbo.
The 4.3L is a solid engine with tons of aftermarket support and is usually readily available for cheap from local junkyards, unlike a Skyline mill which is going to run you well into the thousands of dollars.
Some fab skill and wiring voodoo will be required, but you would have a very unique truck when finished. Plus it would grind the usual "Holier than Thou" purists in all the right ways, which I always recommend!