I think the largest problem you might find is that 2C and 4C engines only really "cross paths" at about the .90 mark. OS and Laser make an .80 4C but that is a really odd size for a 2C. 2C's come in .60's but that is an almost unheard of size in a modern 4C. What would you compare probably the most common engine in the world, an OS .46 AX, to? Satio 1.00 is very common but there will always be doubt if you compare it to a .90 or 1.35 2C. I guess you could dig for a K&B 1.00 ( http://www.mecoa.com/kb/67/9500.htm ) but I think the obscurity of this engine would still leave doubts.

The only real place these engine cross paths is about the .90/91 mark. OS, YS, Jett, Satio, Rossi, Magnum, Thunder Tiger and so on... all make either or both 2C and 4C engines in this size. I think the answer to your question is in the .90's.

Bill