Quote
would it be possible to use the 3.1 pistons and liners in the 2.8 block to get the extra liters?


If the increased displacement is due to bore change alone (and assuming my information is correct) this may be possible. If the extra displacement is due to change in stroke, you'd also likely need the crank and rods. Not much information to go on.

1988 Isuzu Trooper LS
2.8l Isuzu 4JB1-TC intercooled turbo diesel
www.dieseltrooper.blogspot.com