To rule that is 100% the lifters I'd toss in some Lucas Stop Tick and see if the noise goes away a little.
As for a guide to remove them...your going to need to remove the upper intake manifold/lower intake manifold...drain the coolant (which would be first and foremost)...you'll need to remove your valve covers and take off the rockers and grab the pushrods out...then unbolt the lifter guides (2 bolts on each guide...and they stay in the guide...they don't come out)...and then you can pull out the lifters from there...so its basically a LIM/VC gasket job.
At this time I'd get rid of the dexcool and toss in better...cheaper...green or yellow coolant...get new Metal GM Lower Intake gaskets and Felpro Valve cover gaskets. You will also need new rocker bolts since the factory ones are Torque to Yield...which you can get Comp Cam Re-Useable bolts fairly cheap...for like 20 bucks...then you'll be ready for your rocker install later on and you can skip buying bolts there.
