Nice driver upgrade! I have a pair and like them very much. If you are happy with the sound character of the existing horns (JBL 2345, 800 Hz radial horns) why not just drill the 2 required holes. It's really not that difficult. If experience or equipment is an issue, a local machine shop can take care of this in minutes (and yes, a few $'s).

If the drilling is out of the question, consider getting the Altec equivalent of the 2345, the 811. These are regularly available on eBay for under $200 a pair. You would need to damp the horn (there is plenty of damping lore in the archives here and elsewhere). Try to get later production with non-welded vanes, so that destressing (cutting the vanes) is not required. I am using damped and destressed 511's, and they are incredibly smooth and uncolored.

If you want to try something new (and significantly more expensive) you might try wood horns by Martinelli (biradial like your 2345's) or Edgar (round tractrix). Both have a reputation for outstanding performance. Both offer the non-metal/wood sound. The Edgar is said to image very well due to in part to its round mouth and tractrix expansion. Discussions of their sound quality are numerous in the archives here and elsewhere.

Note that differences in behavior in the cutoff region may necessitate changes to your crossovers. Cross that bridge when you come to it. Let us know what you decide and how it turns out!

Enjoy the new drivers!

Bob