I'm getting on to building my motor mount and need some advice on tube size and cross bracing. It's for a Super Stinson Conversion on floats to an O-540.

The Stinson fuselage, where it mates to the engine mounts, is made of arc welded 5/8 .035 and 3/4 .035 which seems light but there are a ton of even heavier O-470 conversions around that are still hanging off those little straws so I want to know if I should be scaling my mount tubes to the airframe and/or beefing up my airframe.

One guy made his from 7/8 .049 which seems overkill but I would love to hear from an expert.

Cheers.