Agree about getting it done ASAP to avoid future issues.
When I built my Model A pickup in California, I used the title for a 30 coupe (along with the running gear for that), a 1-1/2 ton truck cab that was built in '30 (as evidenced by the twist-on gas cap instead of screw on cap.) Of course, I installed a rebuilt engine (from a Model C), and they tried to fine me for not reporting the engine change within 10 days (even though the vehicle had not been licensed for years). I got around that by redoing the form dating it within the previous week. I also needed a "certificate of non-operation" signed by neighbors and a local gas station owner to "prove" I hadn't had it on the road. The Model A's had the engine serial number stamped on the frame at assembly, but unfortunately it was covered up by the body.
Here in Alaska, licensing a car without a title is a giant PITA, either going the "abandoned vehicle" route or getting a valuation from the one guy in the state authorized to do that. DMV here has gotten better, as they have checklists of the paperwork you need before pull a number to get in line. Used to be they waited till you got to an agent, then tell you you need a different form and you got to start the process all over again.
Hopefully Washington is more reasonable.