As a reference it's ~1mm taller than my UDM-SE. With some "wiggling" it should/could fit. However:
I used the startech vented shelf on mine.
StarTech.com 1U Vented Server Rack Cabinet Shelf - 10in Deep Fixed Cantilever Tray - Rackmount Shelf for 19" AV/Data/Network Equipment Enclosure with Cage Nuts & Screws - 44lbs capacity (CABSHELFV1U) https://www.amazon.com/dp/B071KW94ZC/ref=cm_sw_r_apan_glt_fabc_EDR1JDE6N3V21NGD56KD?_encoding=UTF8&psc=1
I have a short depth rack in my basement before I moved to a full sized rack and used shelves like this in it StarTech.com 1U Vented Server Rack Cabinet Shelf - 10in Deep Fixed Cantilever Tray - Rackmount Shelf for 19" AV/Data/Network Equipment Enclosure with Cage Nuts & Screws - 44lbs Capacity (CABSHELFV1U) https://www.amazon.com/dp/B071KW94ZC/ref=cm_sw_r_cp_api_fabc_A5VWFb1R3HDXT
Which were for the OPNSense router and cable modem and PiHole RasPi box.
Rolled steel and pretty sturdy.
Yeah it works great for my needs. Vented and can hold quite a bit.
Use a rack shelf? Probably less expensive than any official Cisco rack mount kit.
https://www.amazon.com/StarTech-com-Server-Rack-Shelf-CABSHELFV1U/dp/B071KW94ZC/
on the cheap, i'd go with ...
https://www.amazon.com/StarTech-com-Server-Rack-Shelf-CABSHELFV1U/dp/B071KW94ZC/
and
https://www.amazon.com/ALITOVE-Transformer-Switching-Converter-Security/dp/B078RTV9C4/
and
https://www.amazon.com/CGTime-Adapter-terminals-Connector-Security/dp/B07MQTCZBG/
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if your devices are all 12v, they'll take what amps they need.
if you need some 9v devices, you can add a buck converter for their plug to drop the 12v down for that particular device. https://www.amazon.com/Adjustable-Converter-1-25-36v-Efficiency-Regulator/dp/B079N9BFZC/
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for more money you can get this beauty.... https://www.altronix.com/products/R1224DC16CB
I used this for a while.
https://www.amazon.com/dp/B071KW94ZC/ref=cm_sw_r_cp_apa_fabc_3pv7Fb31ANMZN
Some quick googling does not bring much up. It seems like they ship with the rack hardware when bought new and are otherwise unavailable.
Posting to the forums and PM'ing the person who responded there may help. They are end of sale though so you may be out of luck.
The alternative is to buy a 1u shelf.
https://www.amazon.ca/StarTech-com-Depth-Universal-Fixed-Mount/dp/B071KW94ZC?th=1
Would this work? I'm thinking of screws and nuts securing the pi's and some sort of wiring holder into position.
If not, then I was looking at this yesterday.