Whadevayado , Pre Glue BOTH surfaces of any joins , wipe off the excess after a while clamped .
A bit of hardwood / ply / alloy / steel ? ? sheet each side , with cardboard under ( between ) so as the paint dost go bunged . Check theres no burrs beforehand . Like glass pin heads . So have it all clean .
IF theres bearers behind the firewall , a scarf joint ( or lap ) to them , about 25 degree to horizontal . and use HEART hardwood ( Rock Maple ? ) Masking each side of whatevers in there , before getting the rasp out ,
you can re mask if you fang it , so you dont scourmark the wood . But a corase file will cut bare timber & likely slide over varnished , final clean to doublers with doublesharp chisel , used like a spoke shave , more or less .
Sounds like a comercial nylon mount onto the bulkhead'd be way easier , maybe a brace Fwd of to bulkhead , so ass it wont loosen . The Folkert in P A M P A has a backplate mount , to copy . Be easyer still , if O S hasem .
file:///C:/Users/PublicInternet/Downloads/SN_Magazine_SEP_OCT_2010.pdf
Precision Aerobatics Model Pilots Association
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1 Oct 2010 — PAMPA Web site. It ... PAMPA Products and/or the PAMPA website. Any ... Here's an actual photograph of the original Folkerts Speed King SK3 that.
bit like this ,

As in a backplate with the flange about a inch bigger circumferance , Lee Machine Shop'd do one , if you wanna spend a pound to save a penny . Better Vibe dispersal ? ?