It needs the following (that I know about):
- VFO knob (I know, it's odd that that would be missing). Encoder seems to turn fine.
- rear (short) RCA jumper
- one oddball internal mini RF cable terminating in a 3 (or 4) pin connector (found by comparing to a "good" IC-735
- bottom feet / stand
None of the items listed are unobtanium, matter of fact, the cables could be fabricated by yourself if necessary.
And a knob does not have to match exactly in order to be fitted to a shaft such that it can work the shaft.
I would likely elect to do the cable fabrication using bits from junkbox and only purchasing that which is absolutely needed in order to check the rest of the rig's operation before delegating it to Hangar Queen partout status.
BTW - cables ending with headers don't necessarily have to have the corresponding header connector in order to be made to work. I have simply soldered stripped wires to the pins on the board or just removed the socket side from the board and soldered direct jumper wires when such are missing. Since you say it is only a 2 or 4 pin connection, that should be relatively easy going. What you need first is the Service Manual and Schematic, likely available as free .pdf download online, then ascertain the point-to-point connections for the thing, find those points in the radio and have at it.