Actually, you have pretty good advice from the ones that know on the BRICKBOARD. George had it right RUST is the enemy.
As far as exchange parts, I found a copy of the Hollander Company cross part interchange manual ( I only have the Volvo interchange section). Its dated 1982. I don't know where you live, but if you are near a large city, with a library that has an extensive automotive section, particullary older copy's of automotive literature, look for a Hollander Exchange Manual.
My copy includes exchange catagories of engine, brakes and wheels, steering and suspension, axel and drive shaft, cooling and fuel, body parts, and clutch and transmission. Under radiator for example they list with or without A/T 62-73. For manual transmition a 67-70 140 or 62-73 1800 MT or 62-68 120 w/B18 engine should fit. However buyer beware, this manual is a guide and I have no information as to it's accuracy. As with all manuals the information supplied should be taken as a guide and you will need to apply your common sense to its application to your project. Above all get a copy of the Volvo manuals for your particular year and model, read them and make notes when you find something that helps your project. Good luck and remember that you aren't the only one who has started a project like this. There are many knowledgeable individuals on the Brickboard who can help, as they have helped me on my project.
I'm Havinfun.