You could save yourself a lot of work, run the cast gear and change the oil to mobil1 (or amszoil)5-30 with a ZDDP additive to get the zinc levels up.
If your bearing clearances are tighter than the old crank the oil pressure will go up. Running a thinner syn. oil will do 2 things:
1) bring the oil pressure down
2) allow more oil to pass through the bearings thus cooling them.
The old adage of running heavy oil - in my opinion - does not hold any value anymore. The shear strength of the syn. is a lot better than the heavy oils without the drag.
