With extension tubes you can be pretty versatile.
The shorter lenses <75-80mm will give the more difficult clearance problems. I've used a 135mm uncoated Tessar on a Nikon bellows & gotten some pretty nice effects, but wasn't looking for swirlies.
You could make a simple adapter with a slot to fit some waterhouse stops and mount a lens forward of that.
The stops can be calculated for any focal length and for what you're doing, close is good enough.
If the adapter is wide enough, you could use a slip fit lens adapter. Mailing tube or PVC will work but cardboard slides much better than PVC. Well you could line PVC with felt or velvet, that would allow smooth adjustment.
Timing, small stops and a lens cap, Galli shutter, or drop shutter will work.
I built a drop shutter with two speeds. IE: two drop plates with different openings, one twice the size of the other.