Laitch -- I get 0.0 when touching the meter's red and black leads in Ω mode, and OL when they're not touching. The resistance between 10 and 5 is OL, and the resistance between 5 and 13 is 0.0.

The temp relay has no impact on the reading at pin 10. Pin 13 is ground.

The coolant sensor is a dual sensor with two wires - one wire goes to pin E of the temp relay and the other wire goes to Pin 10 of the L-Jetronic. You can use any ground or Pin 13 for the other ohmmeter lead.

The temp sensor grounds via the threads.  To measure an uninstalled temp sensor you measure from one terminal or the other to the metal body of it.

See green lines in this diagram:

I wasn't fully trusting the readings on my $10 meter, so I finally got around to getting a nicer one. However, now I'm getting no reading ("OL" / open loop) measuring resistance across 13 and 10. I measured resistance from the temp sensor plug and one of the wires gets 0.0 resistance to port 10, the other sensor wire reads 0.0 at the plug to the temp sensor relay. I cleaned up all the ground connections mounted to that point under the gas tank to make sure they're all shiny/bare metal but it didn't change any of these readings.

I looked at some wiring diagrams available on this site and it seems port 13 should be grounded to the frame under the gas tank. I checked resistance from port 13 to the ground bolt and it reads 0.0 resistance. I also checked resistance from port 13 to the lower battery ground bolt and that also reads 0.0. 

I swapped the temp sensor relay for a spare I have, which made no difference in the open loop between ports 10 and 13.

I also plugged the temp sensor plug into a couple different spares I have, but they all result in an OL reading between ports 10 and 13.

Finally, I checked all the fuses in the fuse box and they all had continuity.

Are there any other grounding points I should be checking, aside from the one under the gas tank and the one under the battery on the left side of the frame?

I recently upgraded my bike to a paralever swing arm, shock and drive shaft. Problem is the rear wheel sits about a half inch to the right of center. I assume this is caused by not having ABS on my K75s and the doner bike having ABS. Does anyone know exactly how far off center it is and what spacer thickness would be needed to get it on center line? Also, would I need longer wheel bolts to make this work?

Given the machine pops on starting fluid it's reasonable to assume we have spark, if the plugs are dry after you've checked Laitch's suggestion then I'd be sticking a multimeter across the injectors and checking if they're being told to inject fuel.

If they're wet & no hint of trying to fire (but if it still pops on ether) then I'd be inclined to check firstly timing & then compression.