If it were my instrument, I'd try using very thin double-sided tape first before making anything permanent. You may not like the other pickup and decide to swap back. Thin double-sided tape can be found in those window insulation kits for winterizing windows with a heat shrink film.

When I designed and installed the adjustable monopod stand for my vintage Stick, I mounted it with 3M VHB (Very High Bond) tape. The tape is very capable of holding the stand, but I installed two very small screws as additional insurance. https://stickist.com/viewtopic.php?f=4&t=16259

I would check with Jeff Mack, there may be more to it than is apparent.

I am looking at two 12 strings that I have, on with a Stickup and one with PASV4, and there are other differences besides the screws. The angle of the two pickups is slightly different, and the Stickup is thinner. I don't know about the ACTV2 Block.

If the ACTV2 is thinner like the Stickup, then you might have another option to make an interface plate that you can mount under the pickup.

But WerkSpace's idea of tape seems like a good starting point.

I would check with Jeff Mack, there may be more to it than is apparent.

I am looking at two 12 strings that I have, one with a Stickup and one with PASV4, and there are other differences besides the screws. The angle of the two pickups is slightly different, and the Stickup is thinner. I don't know about the ACTV2.

If the ACTV2 is thinner like the Stickup, then you might have another option to make an interface plate that you can mount under the ACTV2 that makes it the same size as the PASV4.

But WerkSpace's idea of tape seems like a good starting point.

I just swapped out a PASV4 for an ACTV2 on one of my Sticks, the two blocks are the same size, but the base plate has different hole locations. The Stickup is a different housing. Both of the pickups I interchanged already had holes for both configurations in their respective baseplates, so laying out a pattern to drill was not difficult. I've heard some of the older pickups only have one set of holes, so that might be a challenge. Having both sets of holes eliminates a lot of guess work.



Per Jeff Mack and Gary:

The screw looks like an 8-32.

We use a .148 drill bit for the hole, then drive the screw in by hand. Position the pickup where it should be, mark the holes with a very thin pen or pilot bit just undersized to fit through the pickup housing holes, then drill .148 for final screw holes. Drill as close to the bottom, without drilling through the instrument.

I had misplaced my thread gage, so I asked what the screws were.

Putting and ACTV2 or a PSV4 into a Stick with a Stickup requires removing material from the Stick, going the other way leaves gaps..

After being a long-time PASV-4 user I've been considering trying an ACTV-2, if I can get a hold of one to try out.

If you haven't already seen this, there's some excellent info on all the pickups on the SE website:
https://www.stick.com/instruments/pickups/

Good luck, and please let us know how this goes!