No vapor recovery in 1977 for full-sized Jeeps delivered in the 49 states. California cars and trucks had it. This is shown in the online TSM for 1977, free to read and download. Jeep took advantage of the rules and made the GVWR for all the FSJs above 6000 in this era. The rules were more lax for heavier rated vehicles then.
Yes, you need a vented cap. I use a locking cap that came with my '77. It may or may not be intentionally vented, but it's loose enough now that it does not matter.
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
ECO Green: '15 FCA Jeep Cherokee KL Trailhawk