Good Stuff everyone.
I'd like to add, however, that I've seen 505/2BX cases marked 49cc, (505/1B are marked 47cc), and have the same bolt pattern on the jug as the 505/1B. The mount on the jug where the intake attaches is also slanted like the 505/1B jugs (I think we are using "A cylinder" in this post for that type of jug), but the jug is also square! It does not look like a 1B or 1A jug at all. The pistons found inside are identical to the leftmost piston in the picture above that compares pistons.
A 505/2B is rated at 47cc and has a connecting rod with a different number than a connecting rod found in a 505/1D or 505/2BX or 505/2BY. The number is something like this.
XXXXX 102 XXXX.
The 49cc engines have a connecting rod like
xxxxx 103 xxxx
I have seen them selling on ebay and the 102 (47cc rods) were labled as die kurze, meaning the shorty! I have not measured, but I do think that connecting rods are different lengths between models!!!!
The 505/1B, /2B, /2BX, have a the smaller, bent, slanted mount intake, regardless of square head or not!
That's my two cents.