Hello - We too have a "Fabulous 400" and while we love it, the 40" size may not work with our kitchen re-do plans.
Anyway, remove the right burner and look for an ID plate in that area. That's where our's is. if not there, peak under the other burners. Even when you find the model #, which willproibably be 400-2, etc., dodn't expect much from Tappan. They stopped making parts decades ago.
We got l;ucky and got the repairman from a USED appliance store to come fix ours a few years ago. My suggestion would be to find a store that specializes in USED appliances and try to get their repair person to help, even if it's on a Sunday on his own time.
I don't have a time frame yet..in fact the electrician has yet to give the nod that we can ever do what we want to do..but e-mail me in a few weeks or month and perhaps I'll be able to help you with parts. I found a Fab 400 at a garage sale and took it for parts. I know I have a cutting board and some oven elements in the attic....but I can't let them go until I know what we'll be doing.
Best of luck,