Suitable F valve for a King 2B?

[Splendour]

I have an old King 2B Silvertone that has been rebuilt at some time in the past and looks a little battered and worn, it still plays wonderfully, but I'm not worried about spoiling it's appearance.

Being a bass trombonist I keep finding music I'd love to play on the 2B of it only had a few more notes down the register...
I often accompany small groups and people singing and I have been doing this on an even more battered 3BF when the 2B doesn't have the range, and I've been wondering for a while If it would make sense to cannibalise the 3BF, or if not, what sort of F attachment I would need to suit the 2B.
I have no experience of this sort of tinkering so I'm hoping for some opinions before I commit to anything irreversible.

Would the 3BF valve and tubing (from a .510" instrument) make sense on the 2B (.491") ?
Or would I be better off looking for a smaller bore valve and tubing from somewhere?
Or would transplanting the 2B bell onto the 3BF make more sense or even be possible?

[pompatus]

PM sent.

Aren’t valve sections generally oversized from the bore of the straight horn? If so, is that still the case for small bore trombones?

[JohnL]

I suppose the ideal would be an f-attachment off of an old King Cleveland 605/F. Those were single-bore .491", so the f-attachment should mate up well.

[Matt K]

I have two from a King 3B, which have ports of .530, which are ideal for this. Send me an email if interested in ome. I'm getting to me emails tonight hopefully.

Another good choice is a Yamaha medium bore (448, 646,etc.) Which also have simialr port configurations.

On the more expensive side, Hagmann also sell kits with .530 diameter. I know of maybe three people who have gone that route.

Shires Alto and small bores also are similar but I don't know if they sell them without buying a horn anymore.