The pastor mentions something which I'd like to expand on. A certain large minority of Suntour freewheels are very difficult to crack the bottom cog/locking-ring. This can be overcome by using TWO of the Pedros cassette lock ring tools, plus oversize PVC cheat bars. Even with the latter tools some freewheels are so stuck that it threatens to blow the Pedros tools -- that's where I stop. Amongst my 50 worst/most-neglected freewheels I had only a 4% failure rate when using the pair of Pedros tools plus 3 foot long cheat bars.

The reason I mention all this if that often it is necessary to pull apart quite a number of freewheels in order to come up with the required rings and spacers to build a custom Ultra-6.