1990 Rickey vs 1985 Rickey, money is not an issue, you can have either one with zero financial implications.

You may also make the following assumptions:
-Whichever one you choose, will bat leadoff and have SB setting at 5.
-You are playing in a heavy 1B and HR park with a middle of the lineup full of sluggers
-You have another A++ OF available if 1990 Rickey needs to slide over to LF
-You have a solid 4th OF to cover the missing PAs
-You are planning to score a lot of runs, and 3-2 type games will not be the norm
-The league is uncapped but restricted, he will not face Joss, Maddux, Pedro every single game. There will a mixture of deadball and modern type pitchers of varying ability, but generally pitching will be of good quality.

So there is I think all the info you would need to make a decision! Let's see what you all think! I am quite interested to see how this discussion goes.

Even with 10% less playing time which you say is accounted for with reasonable backup, go with '90 far superior rates. Especially if :

A) his better '85 running game both in volume and success rate is inconsequential since he'd likely score anyway backed by a bunch of bangers, and

I’d go ‘90 every time Even without having the extra PA. I’d run him down to 90% and get to ~700PA with him anyway. His rate stats are better across the board and the defense is close enough.

Every Rickey Henderson season is a disappointment with the exception of 1990 Rickey, who is a freakin’ monster. Bat him 3rd!

To fill in some possible gaps in the data:
It is a DH league.
94 Frank Thomas is batting 3rd, 37 Gehringer 2nd, Rickey's leadoff role isn't changing (8 and 9 hole hitters will both have speed)
The backup OF is a Ken Griffey Jr. season TBD which one.

So I went with 1990 Rickey and here is the final lineup:

1990 Rickey Henderson
1937 Charlie Gehringer
1994 Frank Thomas
1930 Hack Wilson
1998 Mark McGwire
1948 Lou Boudreau
1972 Johnny Bench
1987 Eric Davis
2007 David Wright

1994 Ken Griffey Jr. will play LF when Rickey needs rest. I think I made the correct choice but we will find out!