Sorry for the DP, but I have determined the speedo adapters and cables between my jeep and the suburban are at least similar, I don't have any conclusive evidence to say they are exactly the same, but I will it get by measuring thread pitch and the length of the cable that extends into the housing.
My personal speculation is that jeep used the GM adapter until 87... kinda makes sense in that they used the steering column, t-5 transmission, and pontiac iron duke (until 84/5ish?). My old style speedometer looks nearly identical to the suburban's one, in fact all the gauges are similar. Heck, the TBI system between the two is undeniably similar... Catch my drift maybe?
I'm looking to buy the pass-through pulse generator for GM adapters that was posted here, but first I'll make certain the $50 is properly spent.