Sounds like fun! A handful of us on here have done the gas-diesel swap. It is definitely easiest to do when you have a complete donor vehicle and the space to keep both cars around until the completed swap car is on the road with all the bugs worked out. You will be surprised how many little bits are needed off the diesel to make it all work smoothly! If you're familiar with the innards of the AEL TDI motor you'll have no trouble getting used to working on the D24TIC, they are closely similar in their construction.
The swap is fairly straightforward but it does take quite a bit of time. If this is your only vehicle, you should be prepared to be without it for a while! You can see how I did one here last year:
http://www.d24t.com/showthread.php?t=715
My only hints (which I mentioned in that thread) would be to use as many of the original diesel chassis/electrical/fuel system parts as possible to make things fit together. The result is always cleaner, simpler, and easier if you use the bits that are already made for the job instead of trying to re-engineer the whole thing with a welder and a hacksaw. I've worked on a couple of converted wagons (one 740 and two 960's) that were originally built by a guy who decided he couldn't be bothered to take anything except the engine and trans off the donor car, and equally couldn't be bothered to read the wiring diagrams and figure out how to most easily mate the diesel engine wiring with the gasser body. Those cars were a mess -- poorly fitting engines with home-made mounts, lots of wiring snaking everywhere under the hood, vibration problems from the drivetrain mounting geometry being off-kilter, sloppy welding everywhere, etc. Those cars also had constant electrical issues needing fixed. If the original components are used, the end result can be the car looks and works just like a stock diesel Volvo under the hood -- in fact, if you really do it carefully, it should be impossible for an onlooker to tell that it was ever anything other than an original diesel car! Moreover it saves time and hassle for you, both in assembling it and making it reliable afterwards.
All that said -- it's even easier still to buy an original Diesel in good shape and make it nice. There's a forum member selling one here in the UK in pretty good shape for £300:
http://www.d24t.com/showthread.php?t=1053 Just one alternative, especially if you need to have a running vehicle in the meantime...
Welcome to the forum -- keep us posted on how it goes and don't forget to post pictures!