RE: New Great Planes Revolver
os make pre made, so try the usual places
regarding length , header length is critical (port to pipe) so you will be adding to it with an extension and may need to chop a bit off the header.
mac do an extra long header, from memory, I think this is the ideal size to fit the rev
your fuse mount needs to be as good as standard landing gear mount (it's easy, because you can use the forward servo tray bulkhead as part of this structure)
remember that your c of g with move considerably, I have 6 oz of lead on my engine mount.