Hello all good
your thinking of fitting two 8.4s in place of two 5.7s ... in series . ?
If so , they should fit ok in a series machine , although iv never tried it , so although 6.6s fit that way the 8.4 might be hitting against something space wise . The 7.4 bolt pattern is suppose to be the same as the 8.4 , It might be an easy swap as the 5.7s come fitted within the enforcers 7.4 outer bolts .
As often mentioned though , no big (if any ) difference between the 8.4 and 6.6 performance wise.
I should be playing around with machines and vacs again soon , i could see if they fit .