What year chassis number 1A******

Under the landy today and noticed the rear ns caliper is leaking on my Salisbury axle .
Now..I fitted this axle to my 86 110 7years ago to replace the drum axle and rebuilt the callipers with new pistons and seals at the same time.
I've found the receipt for the caliper kits (stc 1281) but rather than do them again with chrome pistons I would like to use stainless ones instead, I've recently done the fronts in stainless as well.
After googling for ages there appears to be 2 types of chrome pistons , pre and post chassis number 1A*****
But..
Only 1 kit listed in stainless (DA1172).
I can't see how the stainless kit can fit both pre and post 1A**** when normal pistons have different part numbers (and prices!)
Confused I am...
My rear brake pads were STC 1601 and held in with 2 pins/ clips per caliper if that helps identifying my axle year?
Ta for any help, going to have to mail order as she's my only form of transportation and I don't want to risk driving her or ordering the wrong pistons

Well, couldn't wait any longer so took a chance on DA1172, ordered overnight so should be here tomorrow.
Fingers crossed

Kit has arrived and pistons are the same hurrah!
Unfortunately I've found it wasn't brake fluid but diff oil leaking instead.
Got the hub off to identify which seals I need and off to fetch them shortly.
Had to cut the brake pipe off close to the caliper fitting but hopeful that I can reflare in situ if the pipes long enough.
Calipers needed doing anyway , rusty sticky piston in the first one I stripped.
Had to weld a bar to the inside of it to ease it out, 150psi of air wouldn't shift it alone. With hind sight I should have pushed them out with the brake pedal first but I'm working alone , in the rain on a mud driveway .

But I do have a square bit of tatty hardboard luxury notice the trolley jack sunk in the mud.

Looks like a proper landy tool kit - choice of hammers and crow bars, screwdriver with busted handle, measuring jug that the missus hasn't noticed is missing yet.

Hahaha! Yeah...they all have a purpose, jug is catching the brake fluid from the cut pipe, screwdriver with busted handle is great for levering the lock washer tab up, crowbars were being used to ping the multi point spanner off the caliper bolts, well, the front bolt anyway, rear bolt has access for a socket.
Got the new seals , stub axle and hub and the hub complete is now fitted . Going out again after me tea to fit the shiney new pistons and seals and reflare the brake pipe all being well.