Unless you need locking securty application, the RPA 281 is the only choice you'll want to make. And I'll PM you with a better Drop concept soon.
6:00 pm......sheesh, I thought I edited this and posted. never trust a Smartphone!
Using the Chief Drop Pole is a wasted extravagance that actually looks awfully ugly. With the Threaded opening of the CMS115 ($20.00) and using the RMA 281 ($149.00 avg.) you can cut Schedule 40 1.5" PVC Tubing to your exact length needed, glue on Threaded Male Couplings on each end, and make a perfectly rigid Drop that can accommodate the passage of both Electrical and HDMI cordage down the inside...out of sight. And you can do that for all of $10.00. (..oh yeah...you can paint that Tube as well...)
So all told, a total cost of $180.00....give or take tax, and you'll have a far more cosmetic Drop that can be made to "exactly" the drop length you need...and if you want to change it (shorter) if takes a quick cut, a $1.00 coupling, and you good to go.
Hey...I'm a Chief fan of the RPA series. The RPA-U? Totally bogus choice as far as a PJ like the JVC (I have just done two X3s in the exact manner described above, BTW...) The new adjustable Arm channels are horrible things, and they can NEVER be made to be so tight as to prevent the PJ...ANY PJ, from wobbling if touched. That's pretty lousy stuff if one is paying $150.00 plus for a Mount solution.
Chief does sell the 281 PJ Specific Plates separately, but at $100.00, that's a bit insane if a RPA 281 comes complete with both the Mount assembly and the PJ Plate for $150.00.
The older RPU (Universal) Mount can also work, but it too costs $150.00 so it's not really an issue to even consider unless you have one already...and even then, I can tell you that some spacing is required to lift the rear reaching Right Channel Leg over the Bottom Filtered Ventilation Intake...plus you'd need the 5mm screws.
Also BTW, the depth of the Mounting Holes...as in how deep the Threaded inserts are, requires you use at least 30mm long screws.
Sukamar, you can research until this time next year and you won't find a better solution than what I've outlined above. More expensive...certainly. But no better if even "as good".
Peerless? Expect to spend even more. Monoprice? Pug Ugly....flimsy, and certainly both not in keeping with the investment made for a PJ like the JVC, nor effective and dependable enough to warrant risking a $4K PJ that weighs over 33 lbs in an inverted position.