Not to change the subject , but GM did a twin turbo TB as a SS model , it was a concept model and was considered before or with the SS V8 .
Don't know what they had as a PCM in it thought , wish someone could snag that tune from GM would be great to have .
There was someone else that did a vid from overseas that had a single turbo on a 4.2L as well , think they had a problem going into reduced power mode after a few runs .
Here is a link for a V8 reluctor change may work for the L6 :
http://www.goodson.com/technical_sup...ry/PE07_LS.pdf . gives a idea as to what is involved in changing one .