Any “name brand” - Devcon, Loctite, JB Weld, Bob Smith - will work fine. Only thing I’d avoid is the cheap stuff from discounters like Harbor Freight - the quality can be hit or miss. Even the “5 minute” type is strong enough but if you’re concerned about strength go with a longer cure time type.
Scuff the inside of the cone up a bit with some sandpaper, lay in a bead of epoxy, insert your bulkhead and let it cure standing point up - make sure you slide the bulkhead into the cone enough so you can lay in another bead of epoxy with the cone pointed down after your internal epoxy sets up. Regardless of the cure time on the package I’d wait a day between the first (internal) and second (external) bead of epoxy.
Incidentally, IMO the bulkhead mod is unnecessary - recovery failures with that style cone are more about how fits than how it’s shaped, too loose and it can cock sideways and hang up. I do a “fit test” before every flight - with the rocket in ready to launch configuration I lift it by the cone, if it doesn’t separate until it clears the ground it’s ready to go - if it’s too loose I add some tape, too tight remove tape and/or sand. I do this before every flight since plastic and paper expands/contracts at different rates depending on temperature.
But there’s nothing wrong with the bulkhead mod - it’s probably stronger than the plastic cap on the cone shoulder and it looks pretty nifty!
