I am putting a 351 motor with a C6 Automatic tranny in my 79' F100. It originally had the 300 Straight 6. I finally got everything in and went to bolt the transmission to the brace which go acoss the frame of the truck. I had to change the Transmission mount to the one i took off the C4 tranny that was previously in it. The problem is after I have the brace bolted up to the transmission, the brace it self sets back further than it did with the C4. Therefor it doesn't line up with the holes in the frame where it is suposed to bolt up. It is off by a good 2-3". I was wondering if there is a different brace I need to get with the C6 or am I going to have to Drill new holes in the frame. Any help would be great. Thanks

 

If you mount it where it is, don't forget the driveshaft will need to be shortened.

 

Prodigy --
I had to drill a new set of holes in the frame for Harrison - mounted with grade 8 bolts, natch'....

Yes, had to have driveshaft modifed too. My truck was very similar to yours - 6 banger and C-4. I love the 460 and C-6 combo....drives like a dream.