Whiles waiting on the braked you may want to read the threads on bleeding the brakes...may save you some time.

4 ordered

It's easy enough to just fold back the dust cover and measure the piston with some cheap calipers.

Tip: The rear brake adjustment has the greatest impact on the effectiveness of your brake pedal.

Tip#2: back off on all of the front adjusters when you bleed the front system OR use some channel locks to squeeze each piston in as you crack the bleeder of that cylinder to get the last of the air out of that cylinder. But this channel lock thing takes some practice/understanding and may not work for you if you don't do it right.

Yes replace all 4.

64/67 850 Morris- 

Brakes went from 'firm' to ' just pretend you are double clutching'  to 'just pretend you have brakes'. Wife isn't good about pretending.  She didn't want to pretend the car had seat belts either. 

Traced problem easily to leaking Left front wheel cylinder. 

otherwise things look reasonable- lines, shoes, springs all seem shiny. Clearly were redone before I got car. 

Already decided to replace at least the left cylinders -they're cheap and the hassle of getting a seal kit only to find out the cylinder has a flaw that is eating the seals not worth the savings. 

Seem to be 2 different cylinders for twin shoe- early and late.  No #'s are visible on installed cylinders. Original would have been early but given the pedigree of the car I wouldn't bet on it as late cylinders seem to fit too. 

I am inclined to just order 2 late for the left but am concerned that if the right are early then I'll create an imbalance (cylinder bores seem to be different) 

So  crowd wisdom is:
just order 4 and be done with it
mixing and matching isn't a concern- I've done it without issue.
Just pull the cylinder and you'll find the part number (early/late) on the backside (or measure the bore) and replace with like.  -Haven't done this to avoid the mess at this stage.


Probably overthinking this
Be Safe

Kim