Just to fill in a bit more background now that I have the player in hand... this was a ShopGoodwill.com find that I got for $56... it was listed as-is and only tested for power-on, but seemed worth taking a chance (since even PARTS/REPAIR D704s go for well more than this on eBay these days). It arrived today and functionally everything checked out... clear image, both trays open/close smoothly, both sides play, analog/digital/AC3-RF all work. There are some scuffs on the face as seen in the listing picture above, but the white paint deposits from whatever did the scuffing buffed out with some Goo Gone and it's presentable if not perfect (especially in a dark theater room).
As expected from the listing image, the inner jog dial wheel is missing while the outer FFW/RW knob is in place. The post for the inner knob is round on two quadrants, flat on one quadrant, and notched/keyed on one quadrant. I'm pretty sure I've ruled out the CLD-D501/2/3 knobs as incompatible since they're a 1-piece design with a male X/Cross-shaped inner key/hub instead of a notched female hole/slot (man that sounds dirty).
As mentioned before, I'm working with a D701 owner from r/laserdisc that's going to try to confirm the wheels are compatible on both players and attempt to model and 3D print a part based on his own. If that falls through, does anyone have a D704 or similar parts machine they'd be willing to part with the inner jog wheel/dial from? Or a PDF of the service manual so I can identify the part number?
Even if I'm not able to replace the jog wheel dial/knob, this player is a winner and a steal given current prices. I should be able to sell my Marantz LV520 (D504/604 clone) and come out with a bit of profit in the process. I will probably sell the Extron Video Processor I picked up to try to make some gains with the Marantz as well... the D704 with my Marantz AVR handling Comb/AD/Deinterlacing and my projector handling Scaling/Aspect seems to be a notable improvement over the Marantz either with or without the Extron VP. I'm hoping to recoup ~$200 from the Marantz and Extron VP, or maybe even find a local buyer and package the Marantz, Extron, and Rotel RDA-980 (recently replaced with a Denon AVD-2000) for ~$250