Pistons in wheel cylinders can be *really* ugly and still work just fine. There's no sealing taking place against the piston itself--it merely transmits motion from the cup to the pushrod.
Strange how many people seem to be working on these trucks this spring--I've had three pairs of the big truck 7/8" front cylinders in for sleeving in just the last few weeks, when I usually see maybe a pair a year. All were bare castings, so I didn't get a look at the piston type. If yours *are* really bad, and if they are the typical GM type with a conical recess for the end of the pushrod, I've got a bunch of excellent used 7/8" pistons...some of them may actually be brand new.
I'd throw some in with a job, if I had one.
Joe
