New to me 82 GMC Sierra k1500 without rpo codes in glove box

[Jr82gmcsierra]

Hello everyone! First post got a new to me 82’ GMC Sierra k1500 originally with a 6.2l diesel now sbc 350 with np833, which I like. Only a few issues, one being under throttle 3rd gear has some interference which I suspect is a worn synchro. Second and a more perplexing problem for me is my brakes are crap. Hard pedal with very little brake response. I figure the owner before me had the same issue because he replaced the master cylinder, rear brake lines, and rear drum shoes. My main problem is after looking up parts for the power assist booster they only show a diaphragm type when mine is a power steering assist model. They list the kind I have as 83-87 but being a 82’ I’m confused. I’m looking at those because I’ve notice the front rotors barely seem worn like the calipers aren’t working. Tried bleeding the brakes and will try again more thoroughly tomorrow. Any one have similar issues with any remedy. New baby has my time really limited between work and parenting.
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