Ma 12x6x3, modified head,j'en medium plug,10% nitro,-5°c 11300rpm.

Now you're taking. Those numbers look good to me. I think I got 11,550rpm on a 2-blade 12x6, so that's right in line with a little more nitro and an extra blade.

How was the mess coming off the front crank bushing while running?

Not bad mess,muffler leaks,but idont use it in plane,ineed somekind in cowl muffler.
Maybe that, .61-90 size http://www.justengines.co.uk/acatalo...nes_Pitts.html

You will likely lose power if you use a different muffler on the Sportster engine. You could try it though.

Buhahaaaa!! Now iget good numbers.
10%nitro,20% castor,-5°c Ma 12x6x3 j'en medium plug,modified head and 'jen .60-90pitts style muffler with little porting job 11900rpm.

Nice! I'm surprised you picked up that much power! What did you do port work on - just the muffler itself?

Muffler inlet was bad shape and narrow.

Last 2 tanks today ,little rich mixture,nice warm and sunny day 11500rpm,Ma12x6x3.

I have one of these engines I'd be willing to part with and its just like the nib version at the beginning of this thread. No number/size designation just the "G29065" on the mounting lug and then a "2" on the back plate. Its got the motor mount style back plate. Appears to have very little use on it if any. If I dont get any responses here I was thinking about putting it on Ebay but I'm in no hurry.

G29065 K&B