Hi Daniel, my initial thoughts were the same as Dr Zee - what are you trying to achieve? However, looking at a 244 that's on eBay here at the moment I see that it has a single RCA aux send / return with send pots on each channel (yes?), so you should be able to use that loop in the traditional outboard processor manner. And a three head cassette deck should work in the same way as any other three head tape deck, running as a single slap tape echo.
So as a first port 'o call - and at the risk of teaching grandma to suck eggs - I'd try this...
1). Cable from the AUX Send RCA out of the 244 to the input of one channel of the three head deck and cable the output of the same channel back to the 244 AUX return. That should set you up with a loop that's going through the three header.
2). Load up a tape into the three header, keep the three head deck on input monitoring (not playback) to start with and set the input level at say, 50%.
3). Start the 244 and the three header running and adjust the track / master aux send on a track to see if you get a reading on the three header's input meter. Maybe plug some headphones into it to see what kind of condition it is.
4). Adjust the 244 send and 3 header's input levels so the three header's getting a signal that's peaking around 0 db.
5). Switch the three head from input monitoring to tape monitoring and adjust the 244's aux return level until you start to hear the echo coming back into the 244's output monitoring.
Fine adjustments of the individual track aux send, the tape deck's input levels and the 244 master aux send and return levels (if it has them?) could then be made to maximise the echo quality.
Usually the record and playback head of a three head cassette deck are quite close together, (sometimes they are a combo head in the same unit) so I've got no idea how long or short the slap will be, especially coupled with the slow speed of a cassette deck.
For a double slap you could also cable out of channel 1 on the three header into channel 2 then take channel 2's output back to the 244's aux return. It'd double the length of the delay as well.
Dunno if that's what you're trying to achieve or not but it should at least do something audible and controllable when both decks are running and you switch the three header from input monitoring to tape/playback monitoring (assuming there's a tape in there to start with)?
I might have a noodle around with my three header and see what it does when set up in this way.
Geoff