I want to recone an Fi btl ufo style magnet, so which magnet style do I choose on the site forr this? There is new single, old double, and old triple. The ufo features a singles wide slug. Which do I choose for this motor? And how do I know if its universal to impedance?

New single is what you need. The UFO style BTL was replaced by the N2 and there is a specific N2 recone

New single slug as mentioned above, keep in mind that you will need the different spacers for underneath the basket flange if you are changing frame sizes as well.