I think original credit for the trigger wheel swap goes to the late Bruce. There are a few old threads that describe how to install them and use them with the stock ecm to achieve a fast start up. I am only utilizing the 18 tooth wheel with my megasquirt ecm. I don't have the fast start with this setup but I do get accurate and stable timing.
Norb, I think he is running coil per plug ignition or something of the sort with his megasquirt powering it as he posted above.
22#, it would have been great if you took a video of set timing @10° while revving the engine with both trigger wheels as you would really see different timing error since there is such big gap in teeth on the 3x wheel you would see a lot more timing error than the high tooth count.
How would we be able to assure that the timing will be set at a set timing to check the stock ECM? If a custom chip was burned with a flat timing table we could get a good comparison. I have access to a stock ECM/IGN turbo buick but at idle the timing will naturally move around especially if the engine is revved since it is using the stock timing tables. With the Megasquirt and I am sure most aftermarket ECM's you can set the timing static for checking base timing. Also in the MS3 you can set spark latency which will help out with "Spark travel" on low count wheels.