3/32' v 1/8' ?

yeah, that is another concern, the chain tension... supposedly, if i put the shimano freewheel with more tooths, I will need a new chain, since my current one is already at the max tension (i think).

I will search that transmission database, thanks! :)

Do you mean your wheel is all the way in, rather than tension? If you go up by 1 tooth on the freewheel you won't need much extra room so you may not need a new chain.
I also doubt you would have any chainline issues as freewheels must be fairly similar?
And one last point, why don't you just buy another 1/8 freewheel (could even try a Dicta one so it is exactly the same?