IMO galvanized should be banned, and it will be within say ten to fifteen years due it causing water quality problems. Here in Central PA it’s difficult to find any used as drop pipe now and even 3/4″ fittings are hard to come by.
Schedule 80 PVC is a good choice but it can be hard to work with being it comes in 20-21′ lengths. Polyethylene (PE) tubing and insert (barbed) fittings is best. It commonally comes in rolls from 100′ to 500′. We use it to 450′ and sch 80 over that. It comes in variuos ratings; 100, 125, 160 and 200 psi. For any sub pump, I only use 160 or 200 psi rated. For your 120′ well the 160 would be more than enough.
If you don’t have galvanized now and get a 1″ male fitting on a 3/4″ or a threaded 1″ black iron or galvanized pipe long enough to screw into your pitless adapter and add a tee handle, you wouldn’t have much trouble pulling your pump (120′) as long as you had a helper and instructions. If you buy from me you get the instructions and toll free phone support.
I sell the Goulds GS series. You should replace with the same hp and gpm that you have now. If you don’t know or can’t find out what it is, I’d suggest a 1/2hp 10 gpm. Depending on the cable you have, you’d then go with either a 2 or 3 wire version. A 3/4hp might be needed depending on your water usage and the static and pumping water levels and whether you have a cased and screened or rock bore well.
Quality Water Associates