Lifter preload

Sounds like you're doing it right. Once you start replacing factory cams with aftermarket ones that may have smaller/larger base circles, and replacing lifters with non-factory replacements, factory pushrod length may not work, even with factory rockers. Checking pushrod length is the only way to know for sure. Let us know what you find.

btw- when you buy lifters, ask them what their recommend preload range is. They'll likely say, whatever the factory range is, but it's good to make sure.