rd28 engine swap

hello,
i have a rd28 y61 that have at the moment reached 700,000km on the engine but i it's about time that engine changes i am not sure how to go about this i am looking to swap the engine with something that i can easily find it's parts here isuzu is probably the easiest but i am not sure how to go about it any information would be helpful tbh thank you in advance,
from what i've seen the gearbox isn't that loved so do i have to change that if so is there alternative with easy to find parts .
i live in north Africa y61 and y60 parts are starting to become hard to find. isuzu have made a commitment to keep providing parts till 2050 so long term their part are easy to find +we already have a place where they manufacture their engines here can get a 4jj1 brand new for about 8k usd with transmission and everything am not sure if it's worth could check the used market for stuff anyhow i am rambling would love to hear you're ideas about how you would handel this

If the new engine doesn't produce a huge increase in torque and horse power then, maybe an adaptor plate would be a good compromise. You would only have to change the engine mounts. If you go with an Isuzu motor and gearbox, then an adaptor to the transfer case, engine mounts, and a cross member would be needed. You would need to deal with the gear stick and maybe front and rear drive shafts of the correct length too.
Also the clutch slave cylinder hoses would need to be modified too.

Honestly I am not chasing big power mostly something that could do a bit off-road and reliable and could repair it in the next 10 years considering innovation comes late here .
The gearbox could stay for now tbh maybe when I can't repair it I would change it but I am afraid considering how old it is it could be prone to failure some friends told me to get om606 with om603 injectors to make it fully mechanical the engine would cost about 1.2k in USD with a revision it could become brand new but again I am not sure if the gearbox could handle if shit hits the fan maybe look for a zd30 gearbox. The problem here would be if the engine has a problem in the future is how I would have to fix it I am not really optimistic about finding Mercedes parts but I asked around a engine swap for the Mercedes one costs about 3.4k USD (converting currencies is annoying not gonna lie)
I am honestly looking for something reliable with enough torque to be able to go around in the farmland (we have olives farmland) so even from torque perspective it doesn't have to be that much.
Thanks for the clearing up stuff for me appreciate it