Well, the tank I have that is rough fits my John Deere 112 so it may be more work to fit it to your Massey! :fing32:
I do have one of the super long Massey tanks that some idiot let a gas can lean on the fill port and collapsed the neck. One of these days, I may try to fix it somehow with a new neck.
If you are serious and want a tank to practice on, I can send it out to you. Drop me a PM and we can exchange info. I had planned to replace it so if it does not work as planned or if you screw it up, it's no loss. If it works... even better! It's smaller than the Massey tank too. I am also in no hurry at all, because the JD is a longer term project that I just started on.