You might as well check with the person you got your half of the deck from. If the half you have is useless without the other, the other half is uselesser! Since they didn't even know the model number which was printed on the back of the machine, they probably don't even realize what the other half is. Of course the electronics package could have been lost or seriously damaged and tossed, but if the transport works, it's most likely that the other half would as well. It's all solid state and Otari's were built to take it.
If they don't have the unit, it's going to be a nightmare to find one. The picture that I posted was from a mid '70's Otari ad and I've never seen one of those decks before yours. From the configuration and timeline, it looks like it was designed to compete with the Teac 3340s which was a favorite 4 channel deck for home or small studio overdub work. It depends on how you plan to use the deck. If you wish to use it for live recording at home or a permanent location, it might be worth pursuing. If you want to listen to prerecorded tapes, the only ones that will work on that head configuration will be 4 track (Quad) recording which could be fun, but there were very few ever made. You might have to compete with collectors to buy any of these. You could have all new 1/2 track or 1/4 track heads installed but you'd still need to get a repo amp to listen to it.
If you're interested in recording, you'll need a record amp too. You may be able to adapt an old pro audio recording unit like from an Ampex 440, but you'll need 4 channels (if that's how you want to configure it) and while you can sometimes pick these up for a song (under $500 for 4) you might have to do some mods for it to interface with your deck. You may also need a power supply for them (I think it was part of the transport on 440's). Either way, you're looking at pretty close to a grand and that's if the transport works correctly.
The best case is if you want to use it for playback only and the transport is in good shape. One of the requirements for this "best case" is that you're like me and you consider the basic machine as a jumping off point to be molded and configured the way you want it. The stock repo amp would have sounded pretty awful anyway and the heads probably need replacing too. I you don't need the record head, you could have a 1/2 track and a 1/4 track head installed with a switch to chose which head you want to listen through. As far as a repo amp goes, you could get one of Doc's repo amps, build and modify a Seduction phono amp or use one of a couple of other choices (one is to design and build your own as several on this forum have). Believe it or not, there are folks here that are looking for a way to get exactly what you have as far as a back panel connection wired directly to the playback head.
So, the most important thing is to decide how you want to use the deck. The better deck designers realize that there are lots of different applications that tape machine can be used for. If they were seriously into building tape machines and not necessarily into audio, there could be lots of different configurations ( slow speed for data/security, high speed for scientific app.'s, instrumentation recorders and the list goes on forever) and they might not be easily adapted for different purposes.