I am working on converting an old road frame into more of a hybrid/cyclocross with a nubby tire and flat bars, etc for the mountain trails. Along the same lines would be to find a longer spindled bottom bracket that would fit a triple crank. I am trying to figure out about interchanging a longer spindle with existing cups as long as the frame width is matched . . I think it's 70 mm for english and japanese. I know this is very tricky replacing hub cones because of the many different contours of the bearing races that match. It seems like a perfect match on a bottom bracket would be less crucial, but I would like to know if the bottom bracket races are a bit more standardized. Would anyone recommend using a suntour spindle with say Shimano or Tange cups? I am set on using these rebuildable bear always run into problems with sealed cartridge bearings that seem to prematurely develop annoying clicking and cinching sounds.

68mm is more standard.
If you have the "standard" English threaded BB as found on the vast majority of Asian built, non box store, imports, the cups and spindles are "swappable".

https://sheldonbrown.com/bbsize.html

I have a large assortment of SR spindles that would work (sq. taper). If you know the BB width, or more important the crest to crest bearing race width (dimension B on this chart - scroll down to first chart after BCD info). These spindles fit most common BB cups and cranks of the era from the seventies through the phaseout to cartridge systems.

Alternatively, there are many cartridge BBs available if you know what spindle length you want.

Just the thing -- the length of spindle that works with triples seem to be sparse. The spindle there now is around 125.5mm and the small gear on a shallow triple just bottoms out on the chain stay if it were tightened; in that case, it needs a couple more millimeters in length on that side to clear the ring bolts. To be more specific, long spindles are most often asymmetric with the dimensions from the the bearing race to the end. The dimensions on the current spindle is 36 and 37.5mm on the drive side, together with a middle dimension (B) of 52mm adds to 125.5. Right--the frame dimension is 68mm and the tread pitch is eng/jap 1.370" X 24 tpi. FbinNY if you have something of this spec, I would definitely be interested.

here is a picture that has been referred to:

https://www.huskybicycles.com/mm5/mer...t_Code=303-127

You could probably add a 1mm spacer under the DS cup.