Has anyone added a Graflok back to a Mini Speed Graphic? The screw lineup
looks very close, but when I compared both backs, they are not a perfect fit.
So how did you do it? Thanks!

I haven't, but I once bought a Mini that had a Pacemaker type Graflok back to get the back. I swapped it on to my 2x3 Pacemaker Speed Graphic, put the Pacemaker's spring back on the Mini and sold the Mini. So you can do put a Pacemaker back on a Mini.

You'll lose the Mini's flash sync. When the Graflok back was introduced, Graflex offered Mini-style Graflok backs as retrofits. These have a flash terminal at the upper left corner. I've seen Mimis with them.

Thanks for the info.

The Graflok back I have is marked Singer with a cast part number 31711, and doesn't have the flash contact.

After I removed the spring back from the Mini, I found that the screw holes of the Graflok back don't line up exactly with the holes in the camera body. I could attach screws to the top, but the bottom screws would need new holes drilled.

So I'm wondering if there are instructions to retrofit the Graflok back.

A retro fit back was made for the Anniversary. A standard Pacemaker graflok screw holes do not align.
I would take a drill with a side cutting bit or a dremel with appropriate bit and elongate the existing screw holes so that they align with the body. The offset is about 1/2 the screw diameter.
There are no known instructions.
Finding a retro fit graflok will be near impossible.