Anything but a 4.6 will fit in a B&B kit, narrow frame. I think they will make one fit for the right money.
We used a 429 in the B&B. It just weighed a little too much in the front. If we had used aluminum it would have been better. I think the 302 wieght is 55% in the back.
The "5.0 Donor kit" just means everything is in the kit except chassis parts, motor etc.( 74-78 chassis parts) Insted of buying Stages I, II, III As with the B&B kit. Everything is bolt on.
I like the FFR frame and late model suspention. I will most likely go with a Daytona or a Spec Racer. Will probibly be road racing it in the future.
This company goes the extra mile and would use them again.
B&B website