Here's a really good writeup about it.
The XR7 Pickup Identity Case... (so far)
NOTE: Due to the 10,000 character limit I've had to split this post into 2 parts. Also, I guess you need a certain number of posts before your posts can go live instantly. So, for those of you hoping for actual physical evidence, hold onto your shorts, that's in Part 2 Over the years I've seen...letstalkguild.com
I have several Guilds with the XR-7 pickups. On the back of the pickups I've seen 3 things. Some have DiMARZIO PICKUPS MADE IN USA stamped into the plate. Some have the top line ground off so that they only say MADE IN USA and then you have the most common which have GUILD MODEL XR-7 MADE IN USA P/N 90654 stamped into the plate.
I had long suspected that they may have been a DiMarzio prototype or model being discontinued that Guild bought out and had DiMarzio start to stamp GUILD XR-7 on them.
The are a clean sounding HB with no mud in the low end. The HB measures about 8.7K and when you split the coils, the single coil does have the "Class of '55" sound as some have described it. A DiMarzio Tech had told me that the Class of '55 had replaced the VS-1 (DP-108) which were stock in the Guild Detonator.
Anyway, just my 2 cents on what I've seen and heard of them.
Have an X-80 and X-79-3 (at the painters), love these pointy guilds!