Is there any way to convert my 1955 f100 3 on the tree to a floor shifter? If so, which shifter to use?

 

It may take some considerable fabrication to build a mount for it, but you may be able to make this work. I think it would be the best option. There's no direct conversion available that I know of.

Hurst Indy SSA Universal 3-Speed Shifter | Hurst

Personally, I think you'd have to want a floor shift pretty bad to go through the work and expense to make the transition. But that's my 2c.

 

Years ago these conversion kits, tree to the floor, were readily available thru various retail outlets. Floor shifts were the hot ticket. I would suspect there are still some layin' around in someone's stash.