CB750F 75 lowering and clearance!?

[TheDane]

Hi Guys, sorry for my bad english!

Im working on my old CB750, the thing is that I'm going to run with 300mm rearshocks,
and i don't no how much clearance i need to have up to the rear-end??

how much travel will these 300mm shock need without hitting the rear-end!? I'm 161lbs and no passengers!

 

[Jay Ace]

Mine is lowered but not sure by how much, PO installed the rears but I don't think I've ever even come close to rubbing. I'm 220lbs.