Couplers I think are being sold here for a lot less than that..... check for sale add here that says adaptor (but they are couplers.... LOL)
Difference in years..... Yes, the box will "work", however, if you use a pre '73 with pitman arm, you'll need to change your drag link, and all that includes.
For what it's worth, i bought both my manual steering boxes with couplers and pitman arm for 100 bucks. Show a little patience and shop, starting right here on FABO. Perhaps post a "wanted" add.