Frustrating not to have all three Stick pickup modules interchangeable in a common diagonal channel, and with the same pair of fastener screw holes. It's not that I didn't think of it. Who wouldn't? It was a modular design to begin with.

As Greg said, the "Stickup" housing and rear lid are injection molded. Carbon fibers are mixed with the plastic to form a conductive / resistive web for grounding and shielding. This enclosure shields from EMF very well, like a solid metal housing, but without attenuating the high frequencies. Metal enclosures around pickup coils form eddy currents that choke off highs.

I can't reduce the size of the two "Block" modules and still get all the components inside. I could expand the Stickup housing to fit snugly inside the Block channel and such a mold would be a good investment, except that I'd have all this extra empty space inside. I'd be tempted to add electronic features but the whole point of the Stickup design was its simplicity. (I've even been known to remove the volume controls.)

So why not have the Stickup housing CNC machine cut as with the ACTV-2 and PASV-4 Blocks? Thick sheet plastic impregnated with carbon fibers is expensive and very hard on cutting tools.

Adding up these considerations, maybe some of you will understand why in this instance I didn't make the leap to the complete swap concept.

Can't just "pop in" pickups. They must be height adjusted from the bottom to bring the entire module close to the strings. Then adjust the Stickup's Humbucking setscrews for balancing volume of individual strings, or the Block's bar pickups for very close clearances to thinnest, highest pitched strings when they're held down at the highest pitched fret, backing off the height for the thickest, low pitched strings.

For those who want to replace their Block with a Stickup, I usually fasten a Block rear cover plate onto the Stickup's underside and it sits height adjustable right there in the larger diagonal channel.. Not quite right visually but it does the job.

interesting stuff!! As you may know, I'm a mechanics engineer, and I have been experimenting with the pickups on my Sticks. It's my addiction... all my basses have had brain transplants, too The quest for the ultimate tone!
Some 12 years ago, our company got a nice CNC milling machine, and I guessed that the workshop guys could use a test item... so I modelled my own version of the PASV-4 housing, but with different pickup positions, that resemble the Stickup coil positions. It can be heard here:
And more recently, I experimented with a module that houses 3 EMG pickups (2 at the bass side). That one was 3D printed by a friend. The printer took app. 40 hours to finish it... here's the sound of that one:
What all this learned me confirms what Emmett is writing in this thread. For the relatively low numbers of Sticks being produced, a mold is very expensive, and routing becomes more attractive. A routed housing is also very tough. An option for special housings could be 3D printing, but conductive fillaments have their cost and production problems, too... besides that, it's not easy to 3D print a really good looking housing. My housing was printed on a hobby printer, and the surface is pretty rough. Luckily, I asked my friend to print it with 100% material (no air inside), so it's very tough. But pretty? Hmmm.... Industrial printers can give a pretty result, but the price is often higher than milling.

Thnx
If you want the CAD model of the housing, let me know!

I really enjoy the StickUp pickup in #404 and play it everyday thru a Helix Floor into the back of a Roland JC-120 amp, bypassing the JC-120 pre-amps.

I also have a Railboard that doesn't get played very often. It has a superior action but I can't seem to find the same tone as the StickUp. When it comes to a choice of better action or tone, tone wins every time.

I absolutely love the PASV-4, it's my favorite module of the three (RB module not included, of course). I've not tried the ACTV-2 but from the recordings I've heard of the A2, I can get a very close approximation with the P4 and some EQ.

The PASV-4 is just amazing for the variety of tones I'm able to get out of it. I love vintage guitar and bass tones, and with P4 in conjunction with my HX Stomp I've dialed in a Strat-like lead on the melody neck pickup, a fat, hairy P-bass tone on the bass neck pickup, and most recently, after a great deal of tweaking, a killer Geddy/Chris Squire Rickenbacker-like growl with the bass bridge pickup (oddly enough).

I recently purchased a Stickup module with a Block back plate from SE to use if/when I want to record with that classic Stick bass tone, but I don't see myself using it that often because, for my needs, the P4 pretty much covers it all.