The 79-004 is from 1978-79, and its distinguishing feature is the electrical power strip. Other than that, it is sort of a mashup of parts from the Workmate 79-001 Type 4 and Type 6. It cost more than the 79-001 and does not appear to have sold very well, so they are not as common as the 79-001.
What we got in the U.S. as the 79-004 was sold in Canada under an entirely different name -- the Jobmate 3980, even though all of the Workmate 79-001's were sold under identical names in the U.S. and Canada.
I do notice two things apparently missing on yours. First is the feet that come into play when you fold the legs under and use it at its "sawhorse" height. If you look at the attached photo, you'll see a round rubber bumper mounted on the surface of each leg, near its upper end. On yours, I'm pretty sure I see the empty threaded holes that these mount in. If you use yours in that position, the painted legs will scrape on the floor. Those feet were packaged separately, to be installed by the owner, and are sometimes missing because the owner never installed them. Second thing not shown is the 12-foot extension cord that was originally included. This is almost always missing.
As far as features, the 79-004 has those bumper feet and the plastic top-latch levers from the 79-001 Type 6. From the 79-001 Type 4 it has the aluminum H-frame, and from the Type 2 the four screw-in feet at the ends of the legs (for full-height use). Some, like yours, have the dual-layer jaws of the 79-001 Type 4 while later ones have the single-layer jaws of the 79-001 Type 6. The dual-layer jaws can be either plywood, like yours, or veneered MDF. Both of these variations also exist for the 79-001 Type 4.
No parts are available for this model, and I can't tell you whether currently available parts from other models would work.
