Since all the commutator bars are connected to each other through the armature windings, a reading of zero ohms between any two commutator bars is normal. The only way to test for an internal defect is with a growler. At least it's been that way in the 65+ years I've spent repairing starters and generators. Make sure BOTH ends of the battery cables are clean and tight. Even a slightly dirty connector can create enough resistance to create the "no run" condition you're describing. Try removing the new foot start switch and touching the hot cable directly to the copper lug on the starter housing- - - - -that should cause the armature to spin without engaging the drive gear into the flywheel. If that doesn't happen, check the brushes for proper contact with the armature.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!