Proportioning Valve ?

[Ironhorse]

Tried to use the search function but it said the word "proportioning" in proportioning valve query was to long.

My question is:
The proportioning valve on my '71 4x4 with factory disc brakes is leaking at the rear of the valve. All the connections seem tight. I have a '71 or '72 two wheel drive that had a working factory disc brake system before I sold the rear axle and gears. Proportioning valve is still mounted to the master cylinder, far as I know it is still good. Has differant casting numbers but appears physically to be the same. Anyone know for sure if it will interchange? Don't want to pull the one off my running 4x4 until I know that I have one to install on it. Any help is much appreciated.