from the bodging and faffing I've done over the years, the gap between 5/6/7/8 spd cogs has been pretty constant.
The ancient Sachs 6spd freewheel I've used indexed perfectly well with a Shimano 6spd d/t lever until I changed to a friction bar end lever.
The only issue I can think of is the cogs without any sort of tooth manipulation (like shimano's hyperglide) - Some Sachs freewheels I used had little angles on the teeth to allow for smoother shifting. My older Sachs doesnt which results in a loud 'clack clack clack, shift'.
a quick punt around fleabay (not quite your size but with hyperglide style shifting):
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The sunrace one will be ok, I swapped out an old sachs for a sunrace recently and didn't have to adjust anything. 'Fluid Drive Technology' is indeed a treat to behold. Or rather it works fine, much smoother gear chain than the sachs that didn't have any hyperglidey type of thing.
