Would the five speed transmission from 300ci inline six work behind a 302 or 351?
No, a five-speed transmission from a 300ci inline-six Ford will not directly bolt up to a Ford 302 or 351 Windsor V8. The bellhousing patterns are completely different. The inline-six and the V8s have different bolt patterns on their engine blocks where the transmission mates. You'd need an adapter plate (and potentially other modifications) to make them work together, and even then it might not be a straightforward or reliable solution.