forks can probably be revived w/fluid change. Base don your autolube upgrades, you are now downgraded from Super to only Crusty. Honestly, your bike is not "that" rusty. The engine noises might mean splitting the cases though.
Hopefully you get away with only crank bearings, but there are 4 other ones in there too.

I have a DT400C 1976 under resto atm. (dual shock)
And a DT250D 1977 is next after that (monoshock).
DT seat pan ex Vietnam is a non standard option - there isnt much around that isnt rusted to bits.
Yambits and Ebay are your friend.
Email me if you need photos etc This email address is being protected from spambots. You need JavaScript enabled to view it.
Dave

Thanks for the responses! OldBikes4OldMe, I might take you up on some pictures. I haven't quite figured out how best to route the throttle and front brake cables through the handlebars. It seems like the way I have them now isn't quite right.
Pabdt, I think you're right about the shocks. They honestly don't seem that bad off, they just feel pretty mushy at the moment. As far as the engine goes, I think I will leave the bearings alone for the moment. I think they'll hold out until I can get the engine running and sorted out. A DT250 engine just came up for sale near me for $300, but I don't know if I should buy that. I think I could probably get this one going, and who knows what can of worms that engine may be? Is $300 a fair price for an engine? It doesn't look to be in great shape, and it doesn't come with a carburetor or anything.

Even if you have room to store the extra engine… just look at how much parts cost’ ..

Success!
Today I mounted the gas tank and hooked up the fuel line. With a constant supply of fuel, the bike starts, runs, and idles well. I had to mess with the settings on the carburetor a bit to get it to idle. It still doesn't seem to run 100% good, but I think it's good enough for now.
I have a question regarding the clutch; when I put it into gear, it immediately dies and lurches forward. Obviously the clutch isn't doing its job. Is there an adjustment I can do without taking the side of the case off? Maybe just tightening the cable? I want to avoid that as much as possible, but if I have to pull the side I will also rebuild the clutch.
I will try to update again this weekend before I go back to work.

Just roll it along running & pop it into gear then ride it around change up to second & over rough ground on & off throttle & with a bit of luck it'll free. Otherwise only one way & that is 'go in'. Could tie the lever back overnight first but once they're stuck from an extended time sitting they like to stay stuck.

Thanks for the advice! I'll give that a shot. I'm hoping that it will solve itself, but I think it's going to need a little surgery. Fingers crossed.
 

As silly as it sounds, tying the clutch lever to the handlebar overnight often works miracles.  Has worked for me 3 out of 4 times. 

meant hold the lever back to the bar while riding of course cheers

Awesome, I will try that tonight and see if it unsticks. If all goes well it will be technically "rideable"! Next, the seat...