From what I understand, the 300-6 perches are the same as the 360 perches, and are both placed above the crossmember rather than behind it. I currently have the 351W in a truck that had a 300-6...the perches were just moved back behind the crossmember. Problem is, the engine seems to sit higher than it's supposed to.
So when I build this new truck, putting the 351W in place of the 360, I'm sure it will fit if I move those 360 perches back, but I think I'll be in the same boat with the engine sitting to high. I'm hoping I can take either the 302 or 351M perches from other trucks and use those, putting the engine where it's supposed to be.
As far as the 302 HP/weight - the 351W is my baby. I wouldn't trade it for any other Ford motor, as they've been my pride and joy since I've toyed with vehicles. :-) It's currently coupled with a 4 speed. I'm also running 40" tires right now.
Unfortunately, I live in cold-weather-country, and I don't have the luxury of a garage. I'm collecting loads of information and keeping it here for reference, and will be doing a frame up resto starting next summer.