Okay, this ends the multi-part drama around the Eventide Instant Phaser Mk II plugin.
I was having problems with it and looking online found no one else reporting problems.
Digging deeper it turned out to be Operator Error. Mainly, because I didn't realize that the VST cache for REAPER changes between the 32-bit and 64-bit versions. I thought it was just one big bucket I was dumping pointers into. Nope.
So, in the process of figuring this out, I improved my VST hygiene and got the last four tracks, so I'm very pleased to be able to hit the "purchase" button on the Instant Phaser.
Here's the last track I made while sorting out this issue.
No Lyrics - Instrumental