Bruce, MMO is not specified for our airplanes. Ordinarily, Maximum Operating Mach number is only aplicable to jets, etc., but perhaps Joe Harris's airplane has an MMO.
I can't help but believe that any change of "stance" with regard to the installation of 180 gearlegs and 850 tires would have no effect whatever on the tailwheel leaf spring angles. That would be a very small change of angle indeed. Bending the springs in the field might be "common"...but it's not legal without approved data and approved methods to support the modification. The correct springs are either OEM or PMA (which dictates their manufacturing method/material/bend/etc., for good reason.)
There were some Scott tailwheel steering arms which were made of soft aluminum and susceptible to bending no matter if they were installed with tight spring tension or rubber bands.
Replacement with correct steering arms cures the problem.
The compression springs are more likely to compress to the point of rigidity and cause damage to the steering arm and/or the rudder bellcrank. The belief that the compression springs are more likely to improve tailwheel steering on a 170 is in error, because the tailwheel unlocks and casters with much less effort than either type spring offers. (In fact, it's this loss of steering caused by castering that misleads one into believing more rigid steering is desired.)
Get used to using brakes while taxying.