The recommendation to first sort the brass to identify those with the problem,and pitch the short ones might very well be the most practical and the safest choice.
If you don't already know,you can get a hardware store aluminum spacer bushing with a .375 plus clearance hole in it . That and your calipers won't give you a dimension to measure your brass,but you can compare it to other,correct length brass.
Now,as far as recommending "What next?" That's a lot like asking "How thin of ice can I go out ice fishing on?"
The methods you have suggested ,on your own suggest you know what it is you want to accomplish and some methods that may well achieve it. And you have to decide how thick you want the ice to be before you walk on it,because you are the one who will be all alone in the ice water in the middle of the lake if you get it wrong.
If you do decide to try COW,consider you will be spending the money for the COW plus a pound of Bullseye plus primers.
In Ken Waters "Pet Loads",IIRC, Ken suggests about 10% of a normal charge weight in Bullseye,so about 5 1/2 gr.. If I was not getting the results with 7 gr,I'd slow way down.Bullseye is pretty sudden stuff.
You might well have $25 or better in trying to save the brass.
Cheap 30 cal bullets,long seated? I'd guess 170 gr round nose 30-30 might be as cheap as any. Can you get those much cheaper than $18 or $20? A couple dollars worth of primers,powder ? you get about 140 loads for a pound of powder.Thats abouy 18 cents a shot for power,3 cents for a primer,and what?15 cents for a bullet. 36 cents to pull the trigger. How much does new brass cost?
I'm just suggesting do the math on what will be what,three times fired brass?
Good luck!