Just my experience. Chevy springs do well on the ramp, but aren't worth a crap on the trail. Sure they flex, but aren't stable on unlevel ground. I know that from the Hammers. Save your money, and buy USA Springs from Marlin when they get more in. Sure you can save money and buy from Trail Mart, but ask them where they are made. They won't tell you because they are the same as the import springs Marlin has. They are made in China and after one good run, they will not keep their shape. I've seen it.
About how many deg. off camber are we talking about before these things (63's) get hairy? Yeah, man I heard the same things about those imports, good looking out. If I do go with Marlins leafs in the rear they will be the USA's.