Phil.
Do you want neo to save weight, or just to make you amp louder? The main reason people choose neo is because of the weight saving. A Blues junior with a regular speaker (even a pretty heavy one) is still a light amp to carry.
If its the latter then there are a wide range of speakers out there that will do the job. If its volume you are after, its max sound pressure levels you should be looking for (measured in db). When speakers are measured, the standard is 1 watt of power measured at 1 meter with a decibel meter over the entire frequency spectrum. Whatever frequency displays the highest db will give you the spl rating. Some speakers have their peak fairly high in the sonic spectrum which will give you a bright and cutting speaker (one that might sound like it will slice your head off), but not one that necessarily feels fat and powerful. Another speaker might have a slightly lower spl rating, but its peak is in a different part of the eq spectrum and might feel like it has more "punch". Different speakers all have different feel in that respect, so purely looking at spl ratings does not tell you the whole story. The sound, feel and overall performance of a speaker is something you can get clues about from spec sheets, but in the end you have to try them out yourself.
I'd steer clear of a vintage 30 for your purposes. Its loud yes. Its very clear and cutting too, but that is more of a rock thing than a jazz thing for bladting through the mix nest to a heavy handed drummer and a an electric bassist.
If you want your BJ to be a bit louder than currently and sound good for jazz, then go for a cannabis rex. Its not neodymium of course, so you wont get a weight saving, but it is a very efficient speaker (over 100db) and it will do the job of not only making your BJ appreciably louder, but it will fatten up the low end and give a nice full fat tone (something blues juniors are not known for).