Kind of long but here we go! (pictures at end)
The base board is 7-1/4" wide, 39" long, and 1-1/2" thick. This is good because you will want to clamp it to your bench.
My so called "I" block in the rear is 4-1/2" wide, 1-1/2" thick and 4" tall. The two cut-outs are made with the bottom cut being 1-3/4" from the bottom and the top cut being 3-1/4" from the bottom.
Both cuts extend 1-1/2" into the wood and are done on both sides of the blank. The actual vise arms are wood to cut that measure 7" long, 1-1/2" tall, and 1-1/2" wide that fit into the "I" block.
My so called "Block 1" is 4-1/2" wide, 1-1/2" thick, and 1-3/4" tall and mounts right next to the "I" block and is where the butt of the gun will rest up against.
My so called "Block 2" is the same width and height as Block 1 but a 2" door knob hole saw bit was used to drill through the wood with the center point being right on the top height line Before Cutting The Actual Height.
Mount "I Block" 1" from the end of the base board
Mount "Block 1" flush with the "I" block on the front side of it.
Mount "Block 2" 1" in front of Block 1.
The vise hardware is a simple cylinder type of lug that was drilled & tapped for a 5/16" threaded rod. (should be availible at hardware store) this lug was recessed into the bottom of the left side vise arm so that a hole does not show on the top side of the arm. Please note the horizontal slots in both vice arms. They are needed so the arms can open and close.
The vise arms are held in place in the "I" Block by inserting them then drilling a 1/4" hole through everything and inserting 1/4" x 2-1/2" roll pins. this will be the last thing that you do on the vice end.
The front mount (for the forearm) is 4-1/2" wide and 6-1/2" tall. It is mounted 29" ahead of Block 2. I used that 2" door knob bit on this one just like on Block 2 making sure to drill the hole before cutting the height.
Please note that you may want to experiment with the distance of that forearm block as you want the vice to be compatabile with all your Rifles, Shotguns, and you have things like swivel studs to consider.
Block 2, Block 1, and "I" Block are shown left to right
Rear view of "I" Block is shown here.