Guys--you need to go look at the Pinto before y'all start with the endless mods. The stock design has an inverted engine and no bottom cowl. The engine sits in a bathtub. If you just brush the inside of the engine compartment with epoxy (I believe Keith was suggesting that) and then paint the thing--I would use KlassKote--you should be golden. And, no, none of the wood structure is so close to the exhaust ports so as to be likely to burn the finish. I've seen a couple of these fly and was impressed. One had a medallion. Not sure about the other. I grabbed a Hobby Fasteners kit when I came across one a year or so ago. So I'm looking right at the plans. Ain't no cowling in the way. At most, you might scallop the fuse edges there--but if your exhaust ports are front and back the cylinder is still a quarter inch or more from the firewall. If that worries you, just stick on a piece of tin stock right there. My thought is this, if a talented designer was happy with it, it's likely I would be too. (Did you ever see a good rendition of his Excalliber? Wow!) Now, if you go off on a tangent and add a Nobler-looking abomination to the front of the thing, then you have caused a whole new set of issues. Why go there....?
What Dan is not realizing is that if you try to go sidewinder on the skinny full fuse job like the Pinto your tank position will be terrible. You can't line up the fuel mass with the needle in the inboard/outboard direction. So you'll have to set it screaming lean on the ground only to have it go rich in the air. I have had to fix a couple of OPPs (Other People's Planes) in the last couple of years for just this problem.
Don't worry about the orientation of the exhaust ports. It'll be fine.
I just made up a Pinto tank to the Mathis plans for my fellow club member, Mustang Bill. He's got one Pinto he likes and has ambitions to build another. If the tank doesn't make sense just from looking at the plans, then read the article on how you fill it up. It only has two tubes, and no, you don't have to take the line off the needle valve to fill it. My thanks to Mustang Bill for pointing that out to me.
You picked out a great plane. How you have fun with the project!
The Divot
PS--You might want to look up the Barry Baxter article on his 1/2A Stuka in the AMA archives. There's useful info in it for running that engine.