Sounds to me like you know what you want to do but need a little re-assurance from someone, you've got mine. If it was mine I would do the same and put the Saito inverted to keep it in the cowl as much as possible. The only reason for the 45 degree down is for 2-cycle mufflers to exit in a good place, I believe. You will want to keep the 4.5" measurement from firewall to thrust washer at 4.5" even with the Saito or the cowl will not fit. Probably end up with the Saito all the back on the mount with carburetor almost touching the firewall.
Tim