The wood block (plywood is better) works, but adds more weight. For most warbirds that's not a bad thing. It's also easy to mount ignition batteries, weights, smoke systems, etc to the wood.
Lots of people use "standoffs" similar to the ones on the attached web site - can be any length and are recommended by many. One of our club members is a machinist, so I usually just use drilled round aluminum stock cut to length with a large washer next to the wood.

http://www.aerografixs.com/

Hope this helps,

Dave