Quote Originally Posted by dynodon64 View Post
The main reason for the firing order change from the old 302 to the 351, in the H.O. motor, was to take some of the load off of the crankshaft bearings. I don't remember which bearings though.
It takes stress off the front main bearing by not having the two front cylinders fire sequentially. The rear bearing is much beefier as is the block in the rear so it is better able to take the stress. This was more of an issue in the 351 with the longer stroke, I expect the reasons for using it in the HO was partly due to using off the shelf cams from the 351 in the development phase. Once they actually went into production, they could have made whatever cam they needed or wanted. No doubt it was likely also a bit of a marketing ploy to play up the intro of the HO and make it seem better and different from the previous 5.0L engine. Having the 351 firing order wouldn't hurt either for the bearings in the HO, so why not go with it.

FWIW, I chose to use a 351W cam in my 68 302 engine for the bearing issue. At the time I built it, it was pretty hard to find an aftermarket cam with that order, most just sold 302 cams for the 351, Crane was the exception.