Need some help with master cylinder issue in my 58

[ScottH]

Recently purchased a 58 Chevy Apache pickup that has had a camaro front clip and rear installed (believe its from 70s or 80s?). I would like to replace the master cylinder but not sure what to get as a replacement. I've never seen the one that is currently in it (see pic) so could use some input on what to get. Right now the fronts are doing all the stopping (front disc, rear drum). It does have a stock proportioning valve, I'm assuming it came from donor vehicle.

Any info or suggestions would be appreciated.

Thanks
Scott