Rather old thread but I am in the process of replacing the OS 120 in my ST with the Saito 150. Do you have any pictures of how you mounted your 150? If I maintain the spinner to cowl gap I am either going to need to recess the firewall or mount the carb horizontally so that it clears the mounting bolts. I'm starting to lean towards recessing the mount and strengthening the firewall in the process versus the odd carb orientation. Especially since the "velocity stack" will end up outside the cowl in the prop wash.

Thanks in advance