Hi Carlos,
The HDA-65 is 11mm. I don't have any info on the HDA-65, but it would seem to be larger for a 30cc version. The engine will come out lighter then a trimmer after trimming the case. The trick is setting up the case thrust bearing area for low drag. The previous attempts have had low rpm, around 7,000. I think this is caused by drag in the thrust bearing. The intake is reed and the cylinder porting is advanced. Mine is: Exhust 75 degrees BBDC(150 degrees duration) and transfer 58 degrees BBDC(116 degrees duration. Weight should be around 3.5 lbs. The shaft is 5/16x24 thread.

Dave