I recommend installing a 48 and later flathead six, instead of the G series. I have a friend with a stock '47 two door sedan with a G series. Power is not the problem, oil pressure and distributor accesability is. The later H (and M) series engines are a lot better. The one to find is actually the M. This was a bus / two ton truck motor. It is 254 cubes instead of 226 by virtue of its .200 larger bore. H series motor production ended after '51, but M production continued through '53 on F-6 and F-600 trucks. The M block is identifiable by the part number cast into the oil pan rail on the drivers side. If you find a complete, untampered with engine then identification is easy because the M head has the letter M cast as part of the part number and the oil pan has a wider sump that looks tacked on. I had to buy a truck to get my M motor (they are not easy to find). As for split exhaust manifolds, please see my reply about flathead six speed parts a couple of posts back. Good luck and post some pictures!