Hello, I am rebuilding a 67 Galaxie with a meduim case MX trans that has the dual range shift pattern. I have a valve body out of a small case FMX pre 1973 that has the select shift function. I would like to use the select shift valve body in the medium case MX. the medium case trans has a rear pump, valve body has a check valve with a full port opening on the valve body plate. The FMX does not have a rear pump or a check valve. There is a small oriface drilled in the seperator plate. Can I use the FMX valve body in the meduim cas trans and should I put the check valve in it and open the port on the seperator plate??? Not sure what the rear pump function actually is. Seems to only supply pressure when the output shaft spins.  Any help would be greatly apreciated......