....The good book says 6" from the firewall to the back of the spinner...you could probabally stretch that a little.... no more than 1/4" i would say, before things start to look out of shape..that woud give you a spinner rear/cowl gap of about 1/2"..[:-]

I moved everything as far forward as possible, with a Heli " C " spec .91FX and recomended type retracts got the Bear Rare Balanced correctly, ready to fly with an AUW of under 10 Lbs..

I put a lighter Sprung, Sullivan Tailwheel in too..it all helps.