Either would be fine, however the '74 will have the stronger axles as well as a stronger t-case. As long as the chain isn't sloppy, there isn't anything to worry about.
BTW, the '89, if original, should not be full time. It should have the NP208 part time t-case with the planetary low range. Also, the full time case (not used after '79) was not available with a manual trans, with the exeption of the '74-mid-'75 3/4 ton pickup, very rare.
