One reason to leave the block as is and shave the head is because if you end up with too much compression after the head is milled you only have to change to another head and not get into block replacement or piston replacement.
With the right fuel ratio and igniton timing the 9.29 you are calculating shouldn't be a problem on pump gas although you might find it wants 91 octane or more. I'm right around the same compression ratio on my 250 and have always run it on 93 or 91 if that's all available. It might run on 89 but since it runs so good I'm not going to bother to try the 89. I'm also running a manual 4 speed tranny.
