It’s definitely a DJ3. The CJ2A and 3A will have a lot of interchangeable parts. There should be a serial number stamped on your engine on the left front of the block just below the cylinder head. The pre-fix will tell you exactly what it originally came in. It could be the original engine, it is an L134. Check the block around the base of the distributor for cracking. That ruins more of these blocks than anything. Parts are available and you can bore them out to .060 if needed before you have to sleeve it. As far as the 4wd swap, that would have been very easy and it would look factory. The transmission will have a cast model number on the left side, most likely it’s a T-90. The column shifter was originally used in the early post war production run and then later in the non-cj jeeps and the special built surreys and DJ series. Yours has been swapped out for one with a floor shifter and I do see the twin shifters for the transfer case laying on the passenger floor. The transfer case is probably a Dana T-18, there are a few different versions the main difference being the input shaft size. The only thing that I don’t see is the air cleaner which are available used or reproduction. Some pictures from underneath would help to identify what has been installed.