Nick and John - First, thanks for the very kind words and please know that I do usually* try my best to provide the best info I can. That being said, I'm admittedly sometimes wrong and I hope all can forgive me when I muck something up, like I kinda did here. Hope I won't have to stay in the dog house too long for my oops!
My initial info was based on a too quick search this morning that wasn't as thorough as it should have been, and I'll apologize for that and make amends here to set the info straight.
A detailed search this evening of Chevy Master Parts Book resources shows the following (see the excerpt screenshot below):
Front wheel cylinders for your trucks should be GM# 5300869 - 1-1/4" ID, casting# 1074903 (same as those pictured by John above). The Raybestos (and some other brands) used PN: W3406, which corresponded as far as I can tell with their casting# 4810.
Rear wheel cylinders for your trucks should be GM# 5300866 - 1-3/16" ID, casting# 1074886 (again same as those pictured by John above). The Raybestos (and some other brands) used PN: W3396, which corresponds as far as I can tell with their casting# 4806 (again seen in one of John's pictures above).
So what it looks like is you both have the correct front wheel cylinders, given they are in fact 1-1/4" ID, but slightly too large rear wheel cylinders as they should be 1-3/16" ID.
Once again, a huge apology for my roaming off-track and hope this info helps set things back on the straight and narrow.
*
Currently away from home and dealing with a death in the family so my focus sometimes wavers.
