The cabinet volume of the two woofers (I measured each of their internal dimensions) is the same as my Bordeaux speakers (80L). I have taken two RS-225-8's out of my Bordeaux to test in the VR-4's. I did some basic listening impressions last night and tonight, no measurements so far. One speaker had the OEM speakers and the other had the Dayton RS225-8 drivers so I could A/B test them. My first impressions are good. I like the way the RS225-8 sounds vs the originals. The upper bass register seems to fill in a little but which I like. I felt like they were really missing before. This is a minor difference though. You really have to listen in order to hear it.
If I had to find something negative to say about the sound of the RS225-8 as a direct replacement, I would say they sound over dampened with the stock acoustic stuffing. However, I was hearing the full bass range and slightly more of it which is a plus on both fronts. The VR-4's speakers seem to lack bass stock especially compared to my main DIY speakers. Maybe I am acclimated to too much bass. Who knows. Most speakers seem to have a lot more bass in their voicing than the VR-4's. I may take some time to check the capacitors on the crossover boards.
You have to make the hole larger by 1/8". Not a big deal with a sanding drum in a hand drill. The holes are still small enough to easily put the stock drivers back in. It takes around 5 minutes of sanding per hole. I took the opportunity to extend the wires and put spade connectors on the ends. The woofers are not a direct swap but still a good replacement with just using my ears.
Just for kicks, I took some of the dampening material out to expose the rear of the woofer to the port and got the dampening material a few inches away from the Dayton woofers. This seemed to work well with the RS225-8. It made the bass a little stronger. I could see if someone wanted to replace the woofers with the RS225-8 to remove the acoustic stuffing and replace it with acoustic dampening foam.
Again, I have only been using my ears up until now. I plan to take the speakers outside and measure with a calibrated mic. I won't be able to get them up off of the ground to high (maybe around 3') but I can do a A/B between the stocks and Daytons and hopefully omit a lot of reflections. A lot of manufacturers seems to test bass outside even though they have Anechoic chambers. Bass is a tricky devil.
Here is a set of sanding drums similar to what I used. They go in the chuck of a hand drill. There is a 1/8" round-over on the on the mounting hole of the VR-4. I used that as a gauge to keep my sanding even. https://www.amazon.com/WEN-DS164-20-Piece-Sanding-Presses/dp/B07DB2JYB9/ref=sr_1_4?dchild=1&keywords=Sanding+Drum+Set&qid=1614088031&s=hi&sr=1-4
I think this (below) may be the SEAS driver that you see in the newer von schweikert vr4sr. The cabinet shape of those seems to be similar to my Bordeaux speakers which makes me think that the cabinet volume may be almost the same. https://www.madisoundspeakerstore.com/approx-8-woofers/seas-prestige-l22rn4x/p-h1208-8-aluminum-cone-woofer/
The cabinets are almost right at 40l per woofer enclosure (80l total). The ports are 8 1/4" long. Diameter is 3"