There is no standard roll bar for 1973. The first year that the roll bar was optional equipment, aside from the Renegade package, was 1974.
The most common aftermarket installation was the Whitco roll bar, sold as dealer installed special equipment, in 1973. Smittybilts were also available.
Sorry, I don't have one to measure for you. Here's an eBay auction for the literature: http://www.ebay.com/itm/1970-Jeep-Un...-/260327111961
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