I bought a used built block, and it turns out my new crank bolt basically slides in. The owner says he used to have a ATI blower on it and used a bigger bolt (he says it was a 16x2.0 4.5" long). He says he has the bolt he used.

The installer is skeptical of the reason for the longer bolt, and says I need to find a 18mm course thread tap and a matching bolt. Does it matter what material the die is made from? What other details do I need to know? Grade of bolt, 1.5x2.0x2.5 threads, etc.

Any place on the West coast I can still find this to have it overnighted?