Looks great, and I'm considering this exact same setup, taking advantage of the same rear swivel screw nut (I have the same Tikka stock and VA-5 pan head) and drilling a second hole for a screw into a second nut. I have a couple questions (or for others in the know-- @LivetohuntID ?), if you don't mind. How did it work out at the range? I've read some people don't like shooting with a pan head, and having never tried it, I'm not sure why.
Where did you get those M5x8 screws? Does the shape of plate match the contour of the bottom of that part of the stock well enough to solidly attach with just the screws, or would some compound help? As far as fit, any loose play between the rail and the VA-5, or does it lock in pretty tight (I've seen not all Arca rails are exactly the same width)?
Pan heads rotate up and down and swivel side to side. If the ground is not level or the tripod is not set up level, you are unable to adjust out cant in the rifle unless you mess with the legs. When aiming, it has to move in those two directions. So, what makes it good for cameras and glassing makes it less so for a rifle.
Whereas a ballhead moves freely.