Welcome @Guctony! So nice to see another diesel head. There is also an all-diesels section on the forum.
I know exactly what you mean. I searched for years for a 105 without finding anything other than absolute wrecks where they wanted close to 20k USD.
Then I kind of embraced my fate and bought a couple of pretty beat trucks. Just to make you laugh here is a project I call T105:
It has a 1HZ of sorts in it, on mounts crudely welded in. The truck obviously had had a gas engine swapped in and then the 1HZ swapped back in again. The transmission tunnel is awful. Have not really started on it but actually the frame is good and the nice thing about a 1HZ is that it is absolutely rebuildable.
I've found that for me personally the 1HD-T is the sweet spot. Simple as can be with only 12 valves, but with native turbo and improved cooling. I have an 80 with a 1HD-FT and I find it just a shade too complicated.
The one weak spot in the 105 diesel that I have experienced is the use of the R151F transmission. I blew mine up behind a 1HD-T. One of the spacer rings in front of 1st gear literally broke into three pieces. Still did not stop the truck. I would just occasionally pop out of 1st gear.
We are now experimenting with swapping in a H151F but it is not so easy because the shifter position is different on the 100 and most of the salvage yards have H151's from 80 series trucks.
The only other thing I might suggest thinking about is revising your existing R151 with revised 5th gear to drop the RPMs at highway speeds. It makes a huge difference both in fuel mileage and in simple comfort on the highway. That 1HZ really does not like being near 3K RPM. With the revised 5th I'm getting near to 1200 km of range using both main and sub tank.
Congratulations!
And my heartfelt best wishes on your 101. I had an 80 that was really an HDJ81 converted over here in the UAE to LHD. The wiring was a complete nightmare and everything was just subtly wrong about it. Eventually I gave up on it and sold it. I hope your 101 was a better conversion. I would be (and I suspect many others would be) interested in seeing the details on your trucks especially the converted 101. One of the places to look is to pull the kick panels in the front footwells to see what the wiring looks like.