I'm reviving an early 80's Peugeot TH8 with peculiar history and found something curious. Both BBs were assembled by someone with the fixed cups on the left instead of the right. Since French threading used right-hand thread on both sides it is possible to interchange L and R bearing races.

From other evidence it looks like someone had been attempting to upgrade from a Peugeot-branded Stronglight double to a TA triple but never finished the job. One problem that I have now is that the chainnring bolts of the triple hit the chainstay. (This might explain why the attempt was abandoned.) Both spindles are Stronglight 120mm, shown on the Harris website as correct for a TA road-triple, but the proper length for a TA tandem is 127mm.

So I have two questions.

Is it possible that the fixed cup holds the bearings further to the outside? If so assembling them on the wrong side would have moved the chain line to the left.

Would anyone have a 127mm ISO spindle? I believe another 7mm would be sufficient.

Thanks!

Is the spindle symetrical? Try flipping the whole assembly around, or at least dis-assemble it and measure each end of the spindle.
I don't know if ISO spindles work the same as JIS, but 127 is the symetrical equivalent of a shorter size in JIS, can't remember which off the top of my head.
If that's the case, a 127 won't gain you anything on the drive side if the one you have now is in the right way. Then again, it may be that you need the longer length for clearance and chainline on the transfer side.