88 Silverado 1500 Stepside Axle Codes

I'm looking at buying an 88 Stepside. 5.0 Liter (305), auto, pretty basic. No rust, no dents surprisingly. Somewhere in these forumns I found a link for Chevy axle codes, but didn't bookmark it :(, now that I have a list of the option codes out of the cubby hole, I can't find the link. Any other codes would be handy also.
I'm also curious, was an in dash Tach available in these trucks? And what kind of pain in the @$$ would it be to install it?
Thank you in advance for your help.

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