A '72 would have come with 3.73 axle ratio standard, or 4.27 optional. Both are fine for highway travel. If the Jeep is in good condition, you can drive as fast as traffic and your nerve and ears allow. The motor will be fine at those speeds.
With 33s at 85 mph, you'll be turning 3200 with 3.73s and 3700 with 4.27s. A 304 in good condition will run indefinitely at those speeds.
If you do not feel comfortable at those speeds, either you have worn parts or the suspension has been improperly modified. Jeeps from this year were fine at above legal speeds direct from the factory, even with comparatively short tires.
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D