I believe most Massey's have their Serial number plate on the steering column sheet metal, below the steering wheel.
I did go to AGCO and see what engines were used, as far a diesels. It is a Perkins. There should be a tag on..., uh..., I think the left side of the block, below the manifold, with the engine model number.
Looks like the 202's, 203's, and 204's shared a lot of the same parts. Not sure if they just upped the fuel and rpm's for more horsepower, or just what the difference is.
You can go to AGCO PartsBook online, and have a looksee... It's been pretty handy for me to look up part numbers. I've gotten some real good deals on filters and such on epay.
Here is the link to AGCO
AGCO Parts Books
Enter as a guest user. When the next page opens type in your model number (202). You'll just have to scroll down on the next page that appears till you find 202 tractor. I think the 202 through 204 are on the same line.
Not to take anything away from this site, but I have found more guys familiar with the older models on the Yesterday Tractor's site.
There is a fellow by the name of DavidP from Wales, that is a bundle of info on the older tractors...
Here is a link to the YT site.
Massey Harris & Massey Ferguson Tractors Discussion Board
Sign up, and post your picture.., and bet you'll get all kinds of answers..
Good luck..!!