In most cases, enlarger lenses can be used on any enlarger.
The way they attach to the enlarger varies slightly, but most (if not all) of the Beseler enlargers use a very common system - the lens board has a hole and the lens has threads at the back that fit through the hole, and the lens is attached with a threaded retaining ring. The Beslar lens most likely use 39mm threads, which is a very common size.
In other words, it will probably be quite easy to find another lens, that can be used with the same board and ring that is used with the Beslar. Even if the Beslar is an uncommon size, the regular size lensboards and rings are easy to find.
50mm is the standard focal length for an enlarging lens for use with 35mm film. You can use longer focal length lenses, but your image on the baseboard will be smaller, and there is a limit to how long a lens you can both use and focus with.
There are shorter lenses available, but unless they are special wide angle lenses, they won't give you sharp enlargements of your entire negative.
The special wide angle lenses (usually about 40mm in focal length) permit larger enlargements on the baseboard, but conversely are less convenient for smaller prints.
The adjustable aperture is used to adjust exposure. You need that to adjust to different negatives, different papers, and different filter settings. Otherwise, exposure times can be either longer, or shorter than is convenient.
If you have negatives that are hard to keep flat (or paper, for that matter), some extra depth of field can help a bit.
If you are looking for things like lenses, negative carriers, or lens boards, you might want to post in the Texas regional group - there might be someone nearby who can help you or steer you to good sources.
All the best.
Matt
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