I am a little slow...
You are saying you want to put a 4B (or similar) crook on your 3B+ slide, right? I think a single-radius crook, like the 4B crook, would be a good choice. I have a beater 5B slide. If you want, I can pull it out and check the condition of the crook. I don't recall... but the horn, in general, had a long and active life...
That's very kind of you but I have already sourced one.
Bought an early 80's 3B+ today so will know if it's going to work out or not with in a week or so.
Bellend, Just to give you some other ideas....maybe a Bach 42 with no f-attachment or maybe even better a vintage, if you will, a .520 bore 8.5 inch bell Reynolds Contempora or even more interesting Aregnta. I own both and if I was leaning into jazz combo work these would be what I would think would be the best horns in my stable for this kind of sound for me!!!!
I already have an Argenta, an earlier .520 bore one but it's not really in playable condition as yet. Will get it sorted when funds allow. I think the leadpipe is missing any suggestions?