Which arms should I use?

[Jakes-66-K10]

I'm close to having all the parts I need to do a disc conversion on my 1970 CST/20. I have all the donor parts from a 1972 3/4 ton truck. My plan was to install the rotors, calipers, spindles, arms - and everything over to the '70.

I have 4 new 72 balljoints ready to be pressed into the arms. But now that it's come time for this, I'm wondering which arms to press them into? The arms from the '72 are very crusty looking - they'll work, but they scaling off with rust all over them. I think they need new bushings too. The arms currently on my '70 are in great shape, and haven't seen the weather the 72 arms have.

Am I going to create problems by installing the '72 balljoints into the '70 arms? Seems like I heard once that steering radius is reduced... is this correct?