I took a Takagi triple crankset off a bike with a 68mm x 124mm bottom bracket. The bike was from 1983-84 and probably had rear spacing of 126mm or so.

I removed the inner and outer chainrings and mounted the middle chainring in the position of the outer ring. I installed a 73mm x 127mm BB on a bike with a 73 BB shell and 135 rear spacing. There is no way the inner ring would fit without hitting the chainstays and the middle ring cannot even be mounted in it's original location without striking the chainstays.

I want to add the inner ring and make a double. Is it possible with this crankset/frame combination? The 127mm spindle is the longest I found in 73mm. I would need a spindle in the 130's to make it work as a double.

Long spindles were typically asymmetrical. is there any chance you installed it with the short end to the right?

Otherwise, depending on the particular BB you're using, you might b able to put a shim under the right cup, and move the entire unit over to the right 2mm or so.

The BB I'm using is a cartridge so I know it's installed correctly. However, the original spindle may well have been asymmetrical (I just measured it end-to-end). I'll have to look at it more closely later today. I didn't know you could shim a bottom bracket. Is there a specific shim designed for this?

ETA: You nailed it!! The original spindle is 3-4mm longer on the right side!! Is a shim possible with a cartridge BB and is that the most obvious solution (besides a more modern crankset that uses a much shorter spindle)?

IME, old road cranks, don't work well on MTB frames. the geometry of the crank is wrong. the arm is not offset enough from the spindle attachment point and so necessitates BB spindles lengths that are excessive. i've tried it... and failed. but, if you can find a BB spindle that is long enough, (i couldn't, but admittedly didn't look very hard), it should work. there are ways to add a couple millimeters clearance. smaller chainring, spacers on driveside of BB or inside of crank bolts, but they don't add much. take a look at the chainstays on the MTB frame and compare them to a road bikes's chainstays. they sit out much, much further in order to clear wider tires.

i just ended up putting my nice old road crank back on the shelf and lived with the beatup looking MTB crank the i had.

The crank I'm using is an MTB crank but it's literally from the first years of production MTB's. The Suntour parts on the donor bike all have 1983 manufacture dates. I like this bike enough that I think I'll just start looking for a more modern crankset.