Questions about a 2006 5.7

so update, (it says this is the last post even thought I thought I questioned this already) new piston and 4 rods in, new timing set, heavy duty tensioner whatever that does with the stiffer spring, new high volume oil pump, had one valve guide sucked up in the head due to too much carbon on the valve when I changed the seals and cleaned and lapped the valves, took care of that. Got worried so I ordered the new set of MDS lifters so we dont have to pull the heads again, but our manual says you need to change the cam and lifters together when I am looking for the correct locations to put the new lifters in their holders since one set tumbled out in transit..

I got that if you are deleting MDS, but roller cams are hardened, rollers lifters are hardened, why are they saying you treat this like a flat tappet cam? It makes no sense, even though most of this rebuild has not.

So promise, last advice I am looking for, would you put the old set back in that it seems has nothing wrong with them so they stay matched, or replace the knows weak point of this system that makes more sense to me.