The Volvo official factory service manuals are commonly referred to as the "Green Books."
There are several "Green Books," a series, but the one that pertains to the engine is titled:
Volvo
Service Manual
Fault tracing
Repairs
Maintenance
Section 2
D24 Turbo-diesel
700-series 1982-19..
TP 30571/1
6000.11.84
The Haynes manual for Volvo 7xx series is pretty good, but lacks diesel sections.
The Chilton includes diesel sections.
You might try Ebay.
Here is a store I like, dedicated to automotive books; they have shelves of green books:
http://www.books4cars.com/index.php
The D24T is very similar to the VW 1.6, with a few extra cylinders tacked on the end. IP rotates backward, has a different cold start mechanism, vacuum pump is different, Timing belt setup different, cooling system a little different. Most of your skills and tools will transfer over easily.