If anyone else would like to know, support drew my attention to the following section:
"
Due to differences in motherboard layout, the following motherboards are not compatible with the ASSASSIN IV: ROG STRIX Z790-H GAMING WIFI, ROG STRIX Z690-E GAMING WIFI, MSI MEG X570 GODLIKE, MSI B650M APE WIFI, ROG CROSSHAIR X670E GENE, MSI MEG Z790 ACE, ASUS TUF GAMING B760M-PLUS WIFI, ROG STRIX B760-G GAMING WIFI, ASUS ROG STRIX Z690-F GAMING WIFI, ROG STRIX X670E-I GAMING WIFI, and ASUS ROG STRIX Z790-I GAMING WIFI.
"

So it should fit.