The K-B piston is rated at 11-1 when using car heads ,a 4 in stroke crank,and 6.135 rods.With a 3.5 stroke,6.385 rods,and car heads,it should come out to around 10.5 -1 with car ,10-1 with 333's,which would still be a good blower set up IF while doing the work for the bigger valves,you open up the combution chambers for an increase in size to say 25-30 cc's to get to the 9.0-9.5 range.If you cc it during mock up,it might not take much to get you in the compression range that you want.8.5 is lower than you'd need or want given the 5-6 psi of boost than your planning on running.Just my opinion,others may differ.