I dunno---I think after you break it all down into dollars and cents--not only in parts but your labor (you have to put a dollar value on your work---if you don't then I have plenty of non-paying work to keep you busy!!!), you'll be much farther ahead to buy something already running or near running that will not require possibly hundreds of hours to get working right plus painting. For example my buddy and I were partners on a 1998 Lx665 that I found for $1,800 at a trash incineration depot. I sold my interest in it to him for $3,500. All he did was put new tires and rims on it and change the oil. It's now worth about $8-10K.
After it's all said and done you will be left with a machine that has been potentially been weakened by the intense heat.
You might be further off parting it out, and taking that money and putting toward another working one. And while you are at it, from a resale value, and from a parts availability standpoint, trade up to a maybe a 10 year old model which looks better (modern) too.
Don't get me wrong, i have worked on burnt machines, i actually have one more to do. The fire was contained in the engine bay on all machines. It never got past the pump or into the cab.
For me, i didn't put a value on my time as i really didn't have anything else to do. As for weakening, i'm not sure about that, the 743 i did was pretty badly burnt in the engine bay, i cleaned it and painted it too. It has been going for about 4 years now, still no issues with bending or cracking where it got a bit warm. It got a bit warm, the engine didn't melt but the rocker cover did sag a little and totally destroyed the radiator.
If you got the machine cheap and have the equipment, it can be rewarding. If you need to buy most of the parts from the dealer, you may come out worse off i'm afraid. Parting it out isn't a bad idea. Get the engine up and running and you should be able to get a few K there, then pumps and cylinders. This is a last resort if you do your sums and find that parts will simply cost you too much.
Keep us up to date in the progress! I know that in time, the end result can be amazing, i have a machine to prove it