b40 t 150

[big_bean]

i have  what i think is a 1964 350cc engine. i am trying to determine if the cylinder has been over bored. the rust in the cylinder is makeing bore measurement difficult. after beed blasting the piston i find part#41.243.  i have the original spares book which does not have this # in it.  the std. # is 41.242 and first overbore is listed as 41.244. can anyone help?