There are 3 different crank noses. 3.5/3.9 with dissy driven oil pump, then the 3.9 serpy engine, then the 4.0/4.6 version. If you fit a serpy front to the 3.5 the existing key won't drive the front pulley. (The 4.0/4.6 crank needs a spacer under the crank bolt to do up.) I extended a short keyway recently, no big problems. Thread with pics here:
http://www.aulro.com/afvb/technical-...into-94-a.html
Also shows which hole needs drilled for the a/c and alt mount, boss is there, just needs drilled and tapped. Another needs upsizing from 5/16 to 3/8.

