Compatible master cylinders

[Challenger in NC]

the 5-digit number is a vendor code not a part number (Chrysler Corp. part numbers - muscle car era - are 7-digit)

you will find the 18268 on many different Bendix boosters

Was the 18268-8550 version the only one used on a 70 RT (w/383 and disc brakes) or were there others?

[peterro]

How is the pedal travel/feel with that replacement unit? It says it's a 1 1/16" bore. I would think that would make it pretty hard to press for stopping.

[JH27N0B]

I had a 1-1/8" bore mc on my Challenger convertible for a couple years.  It was a Raybestos MC 36283 and was ok, the pedal was a bit hard and I do seem to recall the rear brakes were a little prone to lockup when I had it on the car.
Keep in mind, the OE master for '70 disc E bodies with hemis was 1-1/8 and starting in '71 they used 1-1/32 diameter masters on disc E bodies, so 1-1/16 should be pretty decent if OE appearance isn't critical to you.

[750-h2]

If you want something really close looking to a 2229171, there is a place that seems to have a bunch of NOS A body disc master cylinders.  These look like 7/8 scale 2229171s.  They have the same 1" bore diameter too.  These have pushrods and mounting studs installed, and they would have to be removed to install on a booster.  But the master cylinder itself is the same power or manual.
https://www.ebay.com/itm/NOS-Brake-Master-Cylinder-70-Plymouth-Duster-w-Front-Disc-Brakes-1970/192490888699?fits=Model%3ADuster&epid=1322947189&hash=item2cd159ddfb:g:T0QAAOSwEzxYQZvF&vxp=mtr


Flat front tells you right away that it is not a 9171 MC

[JH27N0B]

I said close looking. The biggest similarity other than having the correct 1" bore, is the hourglass shape on the front, which no aftermarket or later Mopar MC has anything like that shape, with the exception of a 1-1/8 bore B body MC that also has a big fixturing cone machined in the front that Bendix never had, and having used one on my Challenger for a time, wasn't a fan.
If you want something that looks totally correct, you gotta pony up the $600 to $2500 people are asking for rebuilt or NOS 9171s these days.  But for those on a budget and not aiming for OE reference restoration standards, the '5541 looks a lot better than the boat anchors the auto parts stores are selling to service vintage Mopars.