CJ5s were made for decades.
The best frame (foundation) were the boxed frames, which didn't come out till 1977 or 1978. In 1980, federal emissions laws dictated that fuel mileage was a concern (along with Cat Convertors), so the truck transmissions ended in 1979, and (light duty) 5 speeds became the norm. However the transfer case was upgraded to a dana 300 (from a dana 20 or dana 18). There is no perfect year CJ5.
The goods:
Look for a Boxed frame, V8 or fuel injected I6, truck 4 speed manual transmission, and Dana 44 rear axle
The bads:
Early frames were prone to cracks, the carb'd I6 (especally the later versions) were crappy, the automatic (TH400, AMC style) was OK but it was connected to a crappy Quadratrac transfer case, the AMC model 20 rear end was a 2 piece rear axle and had weak axle tubes, but a big Ring & Pinion set.
Other stuff: Look for one with factory power steering and power brakes. WATCH OUT for body cancer (rust).
Good luck.
I loved my CJ5. It was a factory 1979, boxed frame, V8, power steering, power brakes & tilt column. I upgraded it to a 4 speed T18 trans, and Dana 300 tcase, and D44s front & rear. Worked great!
But when I wanted an automatic, there just wasn't enough length to fit everything.
That's a reasonable start for a CJ. Make sure you look at it closely for rust and maintainence concerns.
T