Crank walk does happen, and there are a number of reasons of why it might happen. In the end you can do a number of things to lessen your chance of getting it. 6bokt engines were produced from 90-92, but from a fundamental racing aspect the 7bolt shines in a few areas the 6bolt doesn't (factory main girdle, lighter crank, better velocity head, cam AND crank sensor, etc). Both engines are great, and I think the CW thing is a bit overhyped.
All 95-99 engines are 7bolts, and engines produced for the '99 model year had a revised thrust bearing.
All 95-99 engines are 7bolts, and engines produced for the '99 model year had a revised thrust bearing.