I ended up purchasing a 3-pack of springs and just experimenting. The shortened spring sent with my conversion kit turned out to be unreliable when used with the regular 10mm slide. it would cause the slide to randomly lock back while firing.
when comparing this spring to the original 10mm spring, the difference was very small. probably less than a millimeter total. another thing i noticed when i got the 3-pack to mess with, was that none of the 5 springs i had were exactly the same. tolerances on these springs are loose to say the least.
so for me at least, the tuning process was tedious, but worth it. basically i went to the range with a file, and would take a couple of shaves off of a stock spring, see if it locked back the 22 slide, then see if it caused premature lock backs with the 10mm slide. repeat. Eventually i found the "sweet spot" where it preformed perfectly. (it may also be a little easier to find the common ground with a round other than the 10.

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The place to shave is off the bottom of the short vertical end, not the long horizontal end. And it is VERY easy to accidentally take off too much and cause it to lock back all the time with centerfire slides, so i highly recommend having extras on hand.