Motorman,
It will be tough to fit a 4" crank in. You might do it but you might have to cut it down a bit. A larger bellcrank should tame the plane down a bit because RMs tend to be over sensitive. Most advise to put the push rod in the nearest hole on a 3" bellcrank and even to drill a new one closer to the pivot and to keep the elevator throw down to 25 degrees or so. A longer control horn is also advised (the original was way too short).
I will expect you to be flying your RSM Ringmaster next fall for the 6th Annual Worldwide Ringmaster Fly-A-Thon!!
Have fun!!