A '62 truck had a 283 available as an option. I would just gather the mounts and related parts to fit it. As far as the trans., it could be one of three. A Muncie, a Warner Gear or a Saginaw (you probably have a Saginaw if I were to bet). As far as a 3 speed handling a V-8, I don't think you'll have the traction to tear one up unless you really put a load on.
Just my take on it,
Scott
