These were built as “transmitting” capacitors, so the plates are further apart (breakdown voltage) and larger (compensating for the increased distance). However, they’d work fine as a main tuning capacitor.
https://www.qsl.net/n4dfp/buildcaps.html
An enterprising soul could build a punch and die to fabricate these faster and more uniformly. I’d recommend thin brass plate, rather than aluminum. The former is more temperature stable, dimensionally speaking.
The caveat here is that building a capacitor like this should be undertaken only for the learning opportunity, experience, and satisfaction of being a maker. The cost of even one capacitor, counting iterations to tweak it so that it will work, is much more than buying one. (Per personal experience.)
MFJ has a nice air variable that can be used in a magnetic loop for up 100W. Vacuum variables can be ordered on Ebay for ~$150+/-. Many of the vacuum variables will handle 1KW or more.
Interested in magnetic loops?
Many of the older WWII transmitters had these large air-variable capacitors.
Just last week while I was on vacation in Ohio I visited Fair Radio Sales, in Lima, OH. This is a huge electronic government surplus store with 6 large warehouses on site of old electronic equipment, many of it from after WWII, Korea, and Vietnam eras. The unique thing about this store is that you are free to browse the warehouses at your own pace. Oh, if you are looking for something special they can point you in the general direction…somewhere down this aisle. The aisles are narrow and the racks go up to the ceiling. Grab an old radio, drag it up front and they can help you remove the component you need.
Their website does not do them justice when it comes to what they really have. Most of the time just send them an email explaining what you are looking for. They told me that 98% of their business is via the internet, only about 2% is walk-ins. They have a great technician on staff that can repair and calibrate this older equipment.
I spent about 3 hours there searching for parts to repair some Military TV-7 Vacuum Tube Testers. That’s my hobby, re-conditioning and calibrating these tube testers and re-selling them. I found some parts that they did not even know they had. Every time I am in this area visiting family I always spend an afternoon at this place.