Bicycle Mechanics - help with the bb francais

hi. i have a very old classic french frame. make a long story short it has an english thread bb in there, but somehow its working. i havent serviced the bb since i got the bike. it is now squeaking while climbing and sprinting and i am getting anxious that i should really give it some attention. is it possible to rethread a french shell to english? i thought that english uses a smaller diameter and so a french bb shell could only be made italian, which is larger. if the english bb is just holding in there anyway, does that mean that the french threads are stripped and my only hope is going italian? (i was thinking about getting a phil wood with french rings)...
i guess i should just open it up and see what happens but it sure makes me nervous since ive been putting it off for a while now. i cant afford to make this bike out of order for more than a couple of days... :(

It is unlikely you could thread a R hand thread into a L hand thread if it is a classic
Fr BB, so it may be a newer Fr BB similar to Swiss. The threading is so close otherwise that it is not likely to be a problem on the L side. If you have cross
threaded the R side, unlikely as this seems, it would be difficult to repair as a big
chunk of the threading is going to come out in little pieces. The difference between
24TPI and 1mm pitch is small for less than 6-8 threads, and binding will likely not be
noticeable till 12-15 threads are engaged, which never happens in a BB. Steve

aargh. this is what makes me nervous since the frame is circa late 1940s. it is a follis lyon track frame. i will be around tomorrow when less drunk... any further advice greatly appreciated. gnight.