Lost Rocker Arm Spring Washer, Where'd that little bugger go??? Options

[BeatNavy]

Even though I'm sure my neighbors LIKE the smoke my '72 teener makes when the oil leaks from the pushrod onto the heat exchanger, today I got around to replacing the offending push rod tube seals (cylinder 3). As I put the rocker assembly back on, getting the push rods to seat properly in the rocker arm cups was, as documented in other threads, a bit of challenge for the newbie. When I first started tightening the rocker assembly nuts back on I realized the rods weren't seated properly and started backing them off. But the rocker assembly was under some tension -- the nut came off and the spring washer launched itself somewhere. I don't know where that little bugger went and hid. Not on the heat exchanger, not in my hair, not on my overalls, not on the floor best I can tell. (IMG:style_emoticons/default/confused24.gif)

It's called a spring washer or spring plate, I believe. To me it looks like a plain old washer. It didn't appear to be a lock washer or even have a spring contour to provide tension. These look like what I'm looking for: Type IV Rocker Shaft Nut Kit

My questions: can I run with a plain old washer for a short period of time or something I should be able to get at the hardware store? If not, where's the best place to source? I think my 'teener is getting a little too comfortable on jackstands... (IMG:style_emoticons/default/dry.gif)