Replacement crankcase for a 1995 Evinrude 15hp.

[rixter66]

I am having a bear of a time removing three broken bolts form the exhaust end of my 15hp crankcase. They seem to be welded in and I've tried everything from soaking it in Liquid Wrench to heating the aluminum around the bolts. As far as drilling them out, I wasn't able to get dead center with the pilot hole and am afraid if I go bigger it will dig into the case itself too much. Was wondering if there was an inexpensive source, less than $100, where I could get a used crankcase. I only paid $350 for the whole outboard, so any more than that would be counterproductive to my project. Any help would be appreciated.