Quick Spindle Help.
 

Hey, I'm trying to figure out the proper spindle length for a Shimano 600 English BB and a Shimano 600 triple crank, both 6200 series going on an 1980s road bike. I know the length for the double crank was 116, but how much length gets added for a triple? Thanks for the help!

Hypothetical WAG: if your chainrings are on 5 mm centers, and the chainline for a double is between the two, then when you go triple, you want chainline to be on the center ring. That means moving the set over 2.5 mm. If the spindle is symmetrical, then that means you want a spindle 2.5 mm wider on each side,or 5 mm total. 116 + 5 = 121 mm.

Disclaimer: maybe it's not that simple.

The Shimano small parts catalog lists the FC-6206 (Biopace triple) as using a BB-6207, spindle length..................121.5 for 68mm BB's and 124.5 for 70mm BB's.
Mr Wahl is as correct as you can be.

Great, thanks for the help folks!