I have a 88 tintop i think. It's date coded 12/87 on a plate mounted on the drivers outer side of dash. But it has the square vented cubby hole dash. How and when did they change to a pure 88.5? And how and what can you look at and tell for sure? Thanks 

88.5 was the change over year for the sami.  Basically they were using up all of the stuff from the 87, and gradually replacing it with new 89+ stuff.  89 had all of the new stuff on it.  Or so I've been told anyway.

My 88.5 has the new style dash and newer tranny (different 5th gear ratio), but still had the older style small flanges on it.

 That's strange because i have small flanges too. As far as 5th.gear ratio i don't have clue because it's the only Samurai i have. It does have a aluminum core radiator in it which i read somewere was used in 88.5 and up. It is titled 1988 so i guess thats what it is. Just with a few late model parts added. Thanks