I have a 1999 Legacy which is pulled behind a 2002 Ford Explorer with a 4.0 liter V6 and towing package. Included in the towing package is a posi-trac rear end, 3.73 gears and a transmission cooler. I wouldn't even dream of a using even a small V8. I will buy another 4.0L V6 when the time comes. I have used a V6 without a towing package and it worked but I think it was too hard on the tranny and would cause it to get hot. Nothing an auxillary tranny cooler shouldn't fix.
Doug S.
1999 Supra Legacy