RE: 4-stroke to 2-stroke....
sounds like a 30 size will accomadate in the place of the 50 size four stroke.it says it accepts a 70 size as well which is a 40 size in the 2 stroke sizes. i would put a os 45 max on it, it would scream with that. its going to be roughly twice the ci for 4 stroke. 90 in 2 stroke 120 - 180 in 4 stroke.