Some Jerk Boxes / Blocks bookmarks for later reference
Jerk Block Building Tutorial by Greg Everett
48″ x 24″ boxes, ~ $300
40″ x 24″ boxes, ~ $160
Jerk Box Construction by Les Simonton
40″ x 20″ boxes, detailed construction plans
If you just want Pulling Blocks check out the Stair Blocks.
Here Donny Shankle shows how he constructed the top part of a jerk block.