New member intro and pre-purchase question

Hi forum members! Hello from Seattle.

I'm new to this forum but not new to automotive forums in general. Anyway I've been looking for a good weekend work truck for a while now, and I've found a good candidate, thought I'd check with y'all and see if you have any insight about this truck. I found it on Craigslist (!), the owner has had it for about 4 years and used to be a transmission mechanic. He has about 4 other trucks scattered around his yard but claimed this was his daily driver, and when he came home from work today to meet me, he was driving it.

It's a 1977 K20 with a small block 400 and the TH350. It is almost completely stock. Cheap white steel wheels, non-matching GMC tailgate, aftermarket headers, and a funky dual exhaust that puts the tailpipes between the doors and rear wheels on each side. Other than that it's very stock. It's not too pretty, there are some dents here and there and most of the trim is gone, but the paint isn't bad overall, very little rust, and the interior is pretty clean. No holes in the original seats, glass is all good, everything works. Full-time 4wd. The engine bay is nice and neat, and other than the headers and a new battery, very stock as well. There is a lot of grease on the valve covers and block but nothing you wouldn't expect from an old truck. Starts right up, drives good, shifts smooth, brakes are okay, the seller is offering to put in a new master cylinder for me.

Is there anything specific I should look for that might be trouble later on? I looked over the truck pretty well and saw nothing out of the ordinary. Compared to a 1983 K5 I owned, the truck seems to be unmolested and ready to work. Any tips, warnings, or encouragement you guys can offer will be greatly appreciated. Thanks in advance!

Seller is asking $1400.