What I learned from going with the Micro Switch IVS vs the bus APPS IVS.
Unless you really really want to do the micro switch I would go with Timbo's plug and play bus APPS.
The micro switch IVS requires you to manufacture a bracket and precisely set the idle and throttle values for the APPS IVS. I welded up a bracket after thinking it through for a week or so. Mounted the micro switch, had to make slight further modifications to the bracket, then had to set the micro switch precisely so the trip voltages were very close. Some of the adjustments were less than 1/32".
The micro switch is nice because it separates the two functions, but - not for those that might lack patience. It can be very tedious to get it exactely correct.
Bob Weis
Getting back to basics... 
And MAN, I cringe to bring this up, lest my meaning and intent are misunderstood...
I certainly agree, to the extent that probably MOST guys reading these threads do NOT have the time, patience, and experience to twiddle with this sort of effort as others of us do, and in that regard, Timbo's setup is a clear winner!
BUT, that being said, I *do* want to point out that the primary issue that LED to all this, was the PREMATURE failure of the regular OEM APPS module, and the supposition that the design and construction - as well as the close proximity to damaging underhood heat, was the CAUSE of those premature failures.
With that in mind, I, at least, was determined to abandon the overly complicated and sensitive electronics as used in the OEM IVS section, in favor of something more reliable and less sensitive to underhood conditions.
Obviously the paths of the various "APPS players" went off in somewhat different directions, looking for differing solutions.
In THAT regard, the replacement of ONE electronic IVS device with another, is an unknown, and perhaps a crap shoot - it IS cheaper than the OEM, but in the longer run, is it any BETTER? Worse?
And yeah, the same MAY be true of the purely mechanical MS some of us are using as well - but at least the element of electronic complexity and heat sensitivity IS avoided with a MS, as was the original goal...
Absolutely NONE of what I have just posted is in ANY way intended as knocking Timbo's offering, or the start of a "mines better than yours" debate - just a bit of a reality check to point out that simply swapping one electronics-based device for another MIGHT leave the basic failure issue still remaining - only time and miles will tell.
I just sorta hate for us to take the attitude, or give the impression that all the work is done, and what solutions we now have are IT, and there's nothing more to be done. I have a couple more APPS brackets headed my way, and plan at least SOME added effort to refine and simplify my own particular approach - and to be honest, either I was just plain LUCKY, or else the MS adjustment as used in what I have done was actually quite easy - we'll see if the NEXT version is! :-laf
Meanwhile, and at the very LEAST, Timbo's setup is certainly LOTS cheaper than DC's, and EASIER to install than what I have done with mine!
:-laf:-laf
And truth be known, I sincerely HOPE the Williams replacement APPS meets and exceeds all expectations - THAT would be a clear home run! Oo.
(EDIT!)
ALL my above points WERE valid at the time they were posted, but later dis-assembly and inspection of a Williams APPS module clearly showed that there was NO solid state circuitry used for the IVS function, but rather, and perfectly acceptable, a strip-type switch that is potentially FAR more reliable and resistant to failure, and ALSO noted, was the fact that all internal connections are SOLDERED, and NOT a rinky-dink pressure-pad conductor - so far, so good! 
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