I have been inquiring about this for a while now. I have been told that there is so much custom fabrication just to get the 4G63 in place where the 420a was that its not worth it. I have decided to stay with the 420a and build that into a beast. If there is that much fab work to be done just to get the 4G63 in there think what you would have to do to make it AWD-tranny, diff, driveshafts, etc. Look up my posts about this-alot of info in there