Like a politition. tell the customer what they want to hear.
If you like the plane, fine. But don't use the Z45. TOO HEAVY< VIBRATION LEVEL TOO HIGH FOR THE FIREWALL> you say it has a metal firewall. is it glued, screwed to the wooden one. it better be an entirgral part of the side frames.
If you must go gas then beef up the front end and max out at 2.6-3.2cu.in.
Just a suggestion for your own sake. Learn more about what you are getting into.
Don't take this any other way except as a suggestion to possibly avoid an unpleasant situation.