[mr48chev]

Is the price right for the condition of the truck?

The Hei wire hookup will take all of five minutes to fix before you even leave his driveway, maybe less.
Mufflers equal a trip to your favorite muffler shop but that adds about 150 to the cost so I'd be wanting him to at least split the cost with me. But there is a hell of a difference between sounds great and too damned loud especially with a daily driver.

The gas tank shouldn't be a big deal and a later 18 gallon tank might work better than the original tank in the lowered truck.

I see a lot of rust showing on the bottom side. Is it cancer or surface rust that can be taken care of?
The only way I would come up with a two wheel drive blazer around this area is to build one myself as they are nonexistent locally and the local rednecks go postal when they see a slammed Blazer. Gives me ideas though.