I
love your idea of the pattern transfer wheel. That would be a perfect tool for foam. For small detail work (
including epitaphs), I traced over the pattern hard with a pen and that leaves an impression as well. You then remove the pattern and you can see the impression when you tilt the foam to the light. Then I just re-traced the impression with a pen.
Here's a tracing wheel if no one has ever seen one before:
Here's another tool I used, a Flexicurve. You bend it into the curve you like. Then mark your start and end points on the tombstone and draw your line. Then flip it over and repeat the line on the other side:
I also used French curves to get a good arc going. They can be tricky to use but those curves are great!
I didn't use that template for the overall shape of the tombstone so I don't know how I would scale it other than the old squared method. If you are a bit handy with drawing, I would just use the template as a framework for how much of the foam sheet you can use for one tombstone and design your own. I think it would be easier in the long run.
DarkStar: Thanks
. To be honest, before I started my tombstones I looked all over the net and looked what other people did and took the best ideas and added some of my own. I do that sort of thing for every project I take on. You can call me
The Improver 
That's how I roll....