Interesting vehicle...
You have a BJ42 that was made in Jan1981 but on a different assembly line at the Honsya factory. It was made specifically for the EEC market.
BJ42s only had 4.11 gears (the K082 code on your plate), but some BJ40s came with the taller 3.70 gears, even though they didn't have enough power to pull them.
You have the late body style, but someone has taken liberty with the bezel--you have a late style radiator mount and screen, and late radiator cover (bib) with an early bezel. The headlights have a european pattern that will not pass a USDOT inspection (if they notice). I would think real hard about adding a turbo to a 36yr old engine. If you want to find the weak link on this particular toyota diesel, just bump up the compression pressure and add some more fuel and you too can join the worldwide quest for expensive and dwindling replacement parts. If it is running ok, leave it alone and just use it. It is what it is.
I also noticed from your vin plate, this has the somewhat rare H41 gearbox with the low 1st gear.