I thought you would have learned your lesson about plastic pipe. If you ever want to see that packer jet again, use galvanized. One inch is fine since you won't be able to find 1-1/4" turned couplings. Your jet will work if it is matched to the pump. Which is the one you removed. If the horsepower and number of impellers (1 or 2) is the same.
I don't think you will be getting a lot of water pressure and volume with that pump I saw in your photos.
I would also put the pump back on top of the casing if possible. It will perform better.
If you can't find the leathers, I can send you some. You can find them on my Accessories page. They are called 2" leathers.