I had an 8.8 twin here..We tried it in a F1 Kelly, went 208 mph, don't remember the prop size..The whole front of the fuselage came off in a turn. Archie Snider still holds the Unlimited record set with a larger A cube twin..
if you go to our USRA racing website and log in you can ask about A cube engines and maybe get some parts from one of the users...You will have to send an E mail to the webmaster, we were getting spam and new users must be confirmed..No big deal, it's free and quick..
www.usrainfo.org
Prop manufacturers are there too...