Manual disc brake master cylinder

[mrob]

Hi,
I'm in the process of converting my power disc brakes to manual disc brakes on my 73 Cuda. I've found a few threads about this topic, but didn't see any part numbers for the master cylinder. According to a vendor at Carlisle, he found a Bendix P/N for a reman master cylinder (P/N R11523), but it seems like that master cylinder is very hard to find. So is there another stock-looking master cylinder one that will work?
Also, please refresh my memory - doesn't a manual brake master cylinder have a recess in the back of the master cylinder piston to hold the rubber brake pushrod retainer in place? I remember replacing a manual brake master cylinder (73 Dart), but it was years ago and I can't remember how the pushrod retainer was held in place. I seem to remember a recess in the piston, but I could be wrong.
Thanks!

[Chryco Psycho]

I use the Raybestos 75 dart one , it had manual disc brakes factory .
There is a small rubber oring in the back it locks the pushrod in place , I had actually saved a few of these over the years as spares as they are often damaged on removal .

[mrob]

Thanks Chryco,
I attached a pic with the MP adjustable pushrod. It looks like it comes with the retainer (see red arrow). Is that the rubber ring you're talking about?