Hi,
Being that they only stick out about 3/4 of an inch as you said, try what the other guys said. Do not use anything adhesive as the adhesive may leave a residue on the glass. Do not use a pliers or anything like that due to not being able to feel how tight it really is which can so easily lead to crushing the tube in a split second or cause a microscopic crack which will leak air into it, overload the air or oxygen capability of the getter to absorb it, and destroy the tube in time; be it soon or long down the road. I had KT88 power tubes go that way. They lit up from the inside, burned a beautiful pastle like pink and purple for about 20 seconds, and then died. After a week or so though, they got all powdery white inside as the getter got swamped and could not absorb any more air. As for other tubes used in that brand and model of gear, I had a pair of NOS Mullard 12AU7's and they were as wonderful sounding in all ways as the legends of them describe accurately. JJ makes great sounding 12AU7's as does EH and Ruby. Same for the 12AX7's. It is personal preference, honestly. It can be a massive difference or a subtle and need to listen for it change. They at least tend to be inexpensive unlike power tubes.
Being that they only stick out about 3/4 of an inch as you said, try what the other guys said. Do not use anything adhesive as the adhesive may leave a residue on the glass. Do not use a pliers or anything like that due to not being able to feel how tight it really is which can so easily lead to crushing the tube in a split second or cause a microscopic crack which will leak air into it, overload the air or oxygen capability of the getter to absorb it, and destroy the tube in time; be it soon or long down the road. I had KT88 power tubes go that way. They lit up from the inside, burned a beautiful pastle like pink and purple for about 20 seconds, and then died. After a week or so though, they got all powdery white inside as the getter got swamped and could not absorb any more air. As for other tubes used in that brand and model of gear, I had a pair of NOS Mullard 12AU7's and they were as wonderful sounding in all ways as the legends of them describe accurately. JJ makes great sounding 12AU7's as does EH and Ruby. Same for the 12AX7's. It is personal preference, honestly. It can be a massive difference or a subtle and need to listen for it change. They at least tend to be inexpensive unlike power tubes.