The Engine is mounted horz.
The hatch is 1/8th balsa and just glued on the ARF. I cut the hatch out/off and will replace it with ply after I beef up the firewall. There is also a thin bulkhead that supports the "proprietary" fuel tank. You're stuck using the GP tank unless you remove it.
I bought a Hayes 16oz slimline. Per your instructions I'll be able to pad the tank all over with 1/2" foam rubber. I hope I don't have any fuel tank issues.
What's you best guess "run time" for a Jett 90L on 16 oz's?...... wot