Just use ls7 lifters. Oer lifters only work well if you have adjustable rockers. No point in upgrading from stock rockers unless you are spending the big bucks on adjistables. Just run stock, and measure your pushrod length.
I would switch to titanium retainers with 150# springs. I don't really like the Manley retainers that intense sells. Comp cams makes a better retainer.