As far as your mosin goes, use these. You dont have to remove the extractor.
Now, I haven't seen a field gauge for the SKS. Doesn't mean it's not out there. If you're serious about being done with the C&R life, I wouldn't bother with buying Any gauges for it. With a couple more purchases of SKS's, it would be beneficial. If this is your last one ever.... Then just take it to a smith, who more than likely, has the gauges and they'll give it a once over for your safety. It's better that they do it, because they know what they're doing. Even if you found a field gauge, you could still mess it up, and end up with an unsafe gun.