I found this reference to Dan Armstrong A229D on the GuitarSite web site...
Re: Dan Armstrong Guitars
Posted by: andrewm
Date: November 1, 2007 21:19
"My '69 has the serial number A229D indicating it was the 229th made (so the internet tells me).I purchased it about 13 years ago and it came with a 'Rock Treble' and 'Rock Bass'. Sounds to me Rupert like the pickup you have w/ 'Kent Armstrong' inscribed on it was made after the fact but someone like Mathijs would probably be able to give a definitve answer. I've always wanted one of the white overdrive pickups that you can see Keith using in some of the old footage."
"I love the Dan - I know some people contend that there are inherent tuning and intonation issues with them but I really haven't had that problem and while I wouldn't say they were necessarily versatile in terms of tones/sounds they certainly are perfect for a chunky, buzzsaw crunch (sounds awesome through my Orange head and 4 x 12 cab). Never had the good fortune to try any of the other pickups though."