I have cut stocks of completed rifles to shorten them. You could do it yourself. I'd start with the CVA by tracing the buttplate contour on both sides of the stock with a compass (those things with a point and adjustable pencil arm for drawing circles), using the pencil to mark. Check to see how much that moves the top tang forward. You can cut that off if it looks too long. Have to cut the toe off the buttplate too. Then you have to file the buttplate sides to the slimmer stock. The toe plate can be moved or cut shorter. If all that looks like what you want, scratch a line with the point of the compass to mark the stock both sides. You can tape the off side with clear strapping tape to prevent chipping. Follow the outside of that line when cutting.
Remove the buttplate and toe plate and using a hacksaw with a new coarse blade, 18 teeth per inch, start the cut from the top down, keeping the cut perpendicular by watching the off-side cut, backing up and widening the cut to allow the blade to follow the curve. When you cut as deep as the frame allows, turn the stock over and cut from the toeline. Now really watch the off-side to keep the cut square with the butt. If the curve is so deep that you can't complete the cut, use a coping saw to finish the cut. When the piece is cut off, and the tang either cut short to match the existing inlet or the inlet cut longer, smoke up the buttplate with some yarn wadded up in a cartridge case and wet with paint thinner for a lamp. Fit the buttplate on, cutting down the high black spots with a file, sharp chisel, or scraper made from a screwdriver. Mark the new screw holes and drill for the tang screw about 1/16" forward of the hole center, to draw the tang into the wood. Rear screw goes perpendicular to the plate.
Now you need to file the sides to the wood. The edges will be thicker, so file the back of the buttplate to thin it to the edges so it looks good. If you are really careful, you can avoid having to refinish your stocks.
The Austin Hallek, I'd cut the tang off, it is very long, and maybe the toeplate. Same procedure.
The Lyman GPR, you might want to cut the toeplate, maybe not the tang. So I'd start on the cheapest and least deeply curved buttplate and by the time you get to the A&H or custom Hawken, whatever that is, you will be doing OK. If the buttplates are steel, you can heat them with a propane torch to reblue them, or use some cold blue. Same with the screw heads, which will be filed to fit after countersinking. You can put stock finish on the new cuts before final installation of the parts. Any questions?