I don't have an engine that you'd want to buy at the moment... I have two D24T engines that are not in cars, but one is completely in pieces and the other is still intact but worn out and in "rebuildable" condition, not ready-to-run condition.
I do have the bits to put a turbo on your NA motor. Adding the turbo oil return line to a D24 is not difficult, I have seen two methods personally, both of which worked out fine, and people on here have done it as well so they may be able to contribute more info. To add the supply line, you can install the complete oil filter mount assembly off a D24T which comes with an oil cooler sandwich plate as well as a connection for the turbo oil feed hose.
If you are running low charge air pressures and not too much fuel (i.e. low EGT) just to give yourself an extra boost at higher altitude without trying to add too much power, you may be fine putting turbo bits on a D24 bottom end, as long as the bottom end is in good shape. You can get an idea of the condition of the cylinder bores visually by taking the head off -- you can look for scoring, check for a ridge, and even make bore diameter measurements, all of which will give you an idea of what kind of shape the block is in. However, the only way to test the rings is with a compression test and oil usage measurements. Rings don't respond well to major heat or overheat, as you have discovered in the past...
I had a diesel Rabbit once that was the same way, used a quart every 150 miles after the PO overheated it. The block and pistons were fine, all it needed was a hone and a set of rings and it never used another drop of oil the rest of the time I had it. Easier to do that in a VW than in a Volvo, though, since in a VW you can put set of rings in without pulling the engine out... If yours was using a quart every 2000 before, then that is quite acceptable, but depending on how hot it got it might not be as good anymore now.
Your best bet may be to start by taking stock of what you are working with. You can pull the head, get it checked out, look inside the bores, see what is there. If you see major scoring, or the head is too warped to use, or other fatal flaws show up, then you know it's rebuild time or to look for another motor. If the head is OK and the bores look good, then there is a reasonable chance that you shut it off before it got really hot. If that is the case, the rings could have survived OK and you might get away with a new headgasket, be able to stick turbo parts on it and drive away happy.
You may want to put a post in the Diesel Engine section to get more ideas from others about this and about adding turbo parts to a 240. Several members on here either have done it or are in the process of it now.