I realize that I'm new to posting here, but I thought I'd weigh in on my experiences.

First, I've never had an Ai conversion done by John White. I've heard his work is good.

I have had some work done by "microbe" - Brian Williams. I had him perform an Ai conversion on my 135 2.8 K and 200/4K lenses - using the factory Ai conversion rings that I bought. Both lenses came back to me working flawlessly.

I currently own the following Ai'd lenses (all K lenses that have been converted with factory rings):

20/4
28 3.5 (mostly used with my D200IR)
35/2
50 1.4
55 3.5
85 1.8
105 2.5
135 2.8
200/4

I'm not a big fan of the grind-and-tape method of Ai conversions. I always try to find the factory rings. But lately, these are becoming scarce. Check out Koh's camera, Pacific Rim Camera, and Crystal Camera Repair. They might have the correct rings you need. Best of luck with your search.