I did the PS swap many years ago on my 71 Mach 1. I was fortunate to have a friend that had a good, correct, Saginaw 800 PS box and pump....... until it wasn't and I had to learn how to rebuild them.
The problem is and as mentioned, pulleys. You need the crank pulley and water pump pulley. Again I got lucky and found the correct set, even date code correct, online.
I don't think I have the crank and w/pump pulley numbers, but I do have the correct pump pulley number if that helps. Basically, you need all three correct to get the proper pump speed.
As for PS box, I'm told RedHead are a good company and you can get a fast ratio box if you want. If not, your 71 Mach 1 will need a Saginaw 800 with variable ratio, tag number SPA-T or V, You may also need to replace the pitman arm if you buy a used unit. While in there, check your Idler arm also, in fact check it all and replace anything in need. Do it once, do it right.
Pump hoses; The 71 only had a long hose that goes up over the top of the support brace. Originally I bought a "concours" hose from National Parts Depot. It lasted 10 year, then out one day it blew out of the pump fitting. What a friggin mess!! I replaced the hose with an Edlemann brand I was able to buy through a local parts store. Oh, there is also a small bracket to hold the hose in place, you'll need that too.
One more thing to add to the list. If your car does NOT have a tilt column, you'll need a new "rag joint". I suggest the Lares 201. That can be bought from RockAuto. If it does have tilt, you're SOL I'm afraid, but some have made there own and can help if need be.
