I got mine from Summit but I don't recall the part number. If I remember correctly there are two different water pumps, long and short, but the hose is the same. You just need to be shortened if you have the short water pump.
Actually, now that you say that I think that's where I got mine. I...
I believe the difference with the newer ones is the wiper switch location. It's either slightly off or slightly different size, I don't recall which at the moment.
We don't see many 74 Blazers so make sure you post some pictures somewhere.
I heard he was very good at the work and very poor at the business end of it. I thought at the time if he would just build the harness and charge when done or a very minimal deposit to build it he could have saved himself a lot of headaches. I was going to send him a couple intermittent wiper...
Try GM A body headers. They sit up above the bottom of the frame rails. Maybe try finding a cheap used set for a few bucks on marketplace or craigslist just to see if you can't get definitive info about fitment.
They do and when the USPS gets involved with the package they suck even more. I have an account with FedEx and don't even bother checking the prices anymore. I just go directly to the post office since they have more experience losing packages in transit and can do it for less money.