Rocket Doctor...A '76 CJ-5 should be drum front brakes, the chassis is the first year for a boxed frame, a big plus, the 304 V-8 would be great power for a flatfender CJ-2A chassis. The transfer case is a Spicer 20, rear axle an AMC 20 with the Dana 30 open knuckle up front.
All of the these parts have merit. The transfer case is a through-drive, so it would not line up with the 2A's offset rear axle center section. You could swap the AMC 20 into the early Jeep or install a D44 with a centered diff from a '72-'75 CJ.
The Saginaw gear retrofit would be a real plus over the Ross cam-and-lever steering gear in the 2A. You'd go to a one-piece knuckle-to-knuckle tie-rod and a one-piece draglink ("short tie-rod"), eliminating the 2A's bell crank and twin tie-rods. The D30 front axle, even with drum brakes, is an improvement over the CJ-2A's Spicer 25 closed knuckle.
1976 drum brakes all around would be a major improvement over the 2A's 9" drums. I'd do a dual master cylinder conversion with this brake upgrade, you can maintain the OE through-the-floor pedals if desired.
If you're okay with the AMC Model 20 rear axle (which I like a lot, see my forum topic/post on how to tighten the hub flange-to-axle shaft nuts), you could swap both axles from the '76 chassis into the CJ-2A. There would be adjustments to the spring perch locations and for spring widths in this process; measure the front axle carefully to center it up properly.
I'd want to confirm the degree and caliber of the 304 V-8 rebuild and verify the condition of other pieces (power steering pump, alternator, etc.). The transmission, if the original 1976 unit, is likely a T150, a decent all synchromesh 3-speed that is just "okay" ratio wise with the 2.0:1 low range of the Spicer 20. The 5.38 axle gears in the CJ-2A help offset the crawl ratio limitations and should work with 31"-33" diameter tires.
Of course, you could do a T18 four-speed swap, but this means a conversion and adapter parts if you use the common Ford truck version to get the 6.32:1 compound low gear. This 6.32 ratio was only available with some Jeep CJ T18 units. Most were 4.02:1 first gear.
You'd have the cooling/radiator, 12V electrics, exhaust (rear exit, please, whether single or dual, find a safe way!), fuel supply and other issues to tackle. This is straightforward on a vintage Jeep, though, as each component is simple and easy to access.
If you're willing to do all of this, and if the CJ-2A was not earmarked for a stock restoration, you have a lot of "stuff" here. This buildup would be a time hungry "project", as you know. The result would be a Jeep CJ-2A with much better drivability, handling and highway performance.