Although it is often said that standard 6s spacing is the same between Shimano and Suntour freewheels, I have here a couple of Suntour 6s freewheels that are clearly a bit wider than a Shimano 6s freewheel.

Who knew? It's possible to add shims during a buildup of most Suntour freewheels, but I am pretty sure that these were specified with this spacing at the request of some OEM buyer. Using wider cog spacing can make for more-forgiving shifting action when the ratio spread is wider (as on larger freewheels), since unwanted contact between the chain and next-larger cog than the one you are shifting to is reduced (just as with use of a narrower chain, as 9s chain works so well on larger Ultra-6 freewheels).

There have also been 5s freewheels made with wider-than-standard cog spacing, but from much more recent times, and spec'd exclusively on low-end bikes (ostensibly to improve shifting when lower-quality chain, shifter and derailer parts were used). Threw me for a loop because even modern 7-8s Shimano chain wouldn't work on these without creating huge false-neutral zones within the derailer's travel across the freewheel.

But in most (almost all really) cases, standard 6s spacing IS identical between Suntour and Shimano.

And I am assuming that your rear derailer was Dura-Ace to go with your shifters using both of your freewheels(???).