If you get that resto pack, keep in mind that they will only provide the info on the chassis as it left the factory. In other words, just the chassis and cab, no bed or dump system which can add up to another 3'000 lbs depending on the year and size of box, axle & suspension upgrades, etc. My '56 was listed as a 6'500 chassis weight with a 16K gross, but with the box and add-ons weighs in at over 9,000 with a 21k gross.
There should be a scale around your area, there's always something. Just gotta look around at places like truck stops, shipping companies, feed/seed stores, and make a few calls. You may be able to get it towed, weiged, and get a certified ticket relatively cheap. Just a matter of what it's worth to your sanity when dealing with the DMV really.

If you're not already dealing wih the actual office (instead of a contracted location)you might take it to another DMV office. There's oddly a difference in the people at the desk, the folks you're dealing with may just not care enough to help you out more. Having dealt with he WA DMV for odd projects on several occasions, I know that's petty common.