The OS is not worth the trouble, keep it for the carb which will work on some other engines like Magnum.
I personally would not use the plain bearing TT as it does not have the power of your OS.
There are a lot of really good choices to be had in that size range, one choice would be a Super Tiger 51, same size as many 40-46 engines but strong. It does require a fair ammount of break-in.