i dont think you will have to cut the cowl for the 1.80. if you down load the updated manual it shows a setup with the big saito.
go back a few post and you wil see the link

FYI--- From the firewall to the end of the prop hub 5-1/2 inches works for my OS 1.60
it appears that anything from 5-1/4 to 6 inches will work OK




zonk