The Camaro/Firebird and FWD "3800" models all have a 60-deg bellhousing bolt pattern with starter on the correct side to mate up with an Isuzu MUA 2.8 (or 3.1) V6 5-speed or an automatic with the correct bell housing.

If your clearance issues between oil pan and front diff are during installation, just unbolt the axle-to-frame bolts (2 per side) on the front axle/diff assy and let it drop down for more clearance.

If it's more of an in-place problem (i.e. just won't fit), you'd need to modify the oil pan for proper clearance. Probably gonna have to do something with the oil pan in any case.

Older RWD 3.8's had, if I recall, a B-O-P (Buick-Olds-Pontiac) bell housing pattern and that'd be a different story.

HTH.......ed