Ill guess at this. You have about a 2% chance that you could do that. A 3.8 block is made to have a 3.800 bore with say around .200 thick cylinder walls , when you bore it .200 then the cylinder walls are down to .100 thick and thats not enough. However there were a few 3.8 blocks (badges and part numbers) that were actually 4.1 castings with much heavier cylinder walls. Have it sonic checked and talk it over with your engine builder. Mike