are you doing OC trimix? if doing it in OW and not squeezing through stuff, it may be easier to strap to one of your primary bottles than to try and butt mount it. The 13's are big, use your can light dimensions for relativity or go to home depot and get a short section of PVC pipe. 3" schedule 40 at 14" long will roughly simulate a 6cf w/ valve, and 4" sch40 at 16" long will roughly simulate an AL13 w/valve.
This is an al6 from
@rjack321
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One thing you can also think about is putting an inflator hose on your deep deco bottles and using that for inflation. 50% is a common bottle to get an inflator hose if diving OW where you aren't dropping things off. If you have 32% with you, that's obviously better