Funnily enough, I was looking at these very shocks! Since my AC-1 has adjustable rear travel, I would think fitting a shock with a longer stroke *should* be OK.
Found this on ebay, look OK?
https://www.ebay.co.uk/itm/Rockshox-monarch-plus-rc3-/313544284290?_trksid=p2349624.m46890.l49286