Thanks for the replies all. I've held off until I could find a ...conventional... means to do this. This is a royal pita to get to - (with the leading link forks it is really tight to pull the radiator with the forks on), and we have a 5000 mile trip coming up in a couple weeks; I would not relish trying to repair this in the middle of Kansas...
Re: Motosense; I tried contacting them a few years ago now. Would have loved to go that route. Several emails went un-returned over at least a month period. I called twice; both times I was told to send an email...??? I finally just gave up. I'm glad others had a better experience. Obviously, YMMV.
Back to this stoopid BSP thread sending unit...
Found an adapter - 1/4" NPT to 1/8" BSP - on Amazon.
Drilled the hose adapter for the 1/4" NPT, and tapped it deep. Screwed in the adapter, screwed in the sensor. It all fits well - kind of.

However, the sensor is now out of the hose cross-sectional area by maybe 1/2". I'm thinking this should still work - although with the sensor in a "hole", it may not react as fast as if it were directly in the cross-sectional area. I will be mounting it facing "down", so am not too concerned with a air pocket.

I can still put a plug in this thick-wall area of the hose adapter and tap the other side. The material there is about 1/4" - it should work. But the sensor would still be out of the waterflow area by maybe 3/16 - better than 1/2"...
It's like I need a 1/8" thin wall stainless steel adapter tapped directly for the BSP sensor.
BTW, when I ordered the pipe to BSP adapter from Amazon, I also ordered a BSP tap - although the only source was in China.... The tap delivery is expected between Jul 20 and Aug 7. WTF??? Checked around town yesterday at a few specialty tool places. Only 1 out of 3 knew what I was talking about... and he said he thought he could order one... but the east coast was closed... and he told me top come back next week.
Anybody had good/bad experiences with the sensor out of the tubing cross-sectional area? Why would this knucklehead company make a sensor less than 1/2" in length???