The 351w and the 302 use the same motor mounts and the same bellhousing.
The only transmission change that is required when swapping to a 351w is the balance of the flywheel.
A 351w will need a 28oz flywheel.
Most 302's use a 50oz flywheel.
I have all this and much more on my site, listed in my sig.
I would post it, but I can't access my site from work.