Typically don't need lash caps or hardened tips unless it's titanium or a hollow-stem stainless valve.  600 lbs of open spring load isn't enough to hurt a stainless valve, unless there was not enough lubrication. 

I'm leaning toward an incorrect heat treat on the valves.

Can a hydraulic roller be reliable in the 6500-7000 range.  ?    Existing combo wants to run to 6500 with a flat tappet and want to duplicate that without fear of cam failure.  I really don’t mind a solid flat tappet if it can be made reliable with today’s offerings

Yes.  I have many hydraulic roller engines out there in that rpm range. 

Towd56, a member here, has one of my 390's with a hydraulic roller in his Galaxie wagon. Has made over 250 passes and has put 4000-5000 miles on it.  Launches at around 5000 rpm, shifts at 7000.  Factory non-adjustable rockers.

Solid flat tappets can certainly be reliable.  Pretty easy with a good lifter, such as a Crower EDM lifter. 

Sounds like the blocking ring/gear teeth are not getting along. 

First though, what trans fluid are you running?

Normal.

Since Edelbrock owns Comp Cams, you can pretty much bet it's ground by Comp Cams.   But I've never used one. 

One side note that I'll throw in here:  I've sold a couple hundred cams in the past year or so and not one single one of them has been on a 110 LSA.  The 110 LSA is about as universal as it gets, in an attempt to find a cam that would kind hit the high spots of a bunch of different engines.   With the onset of higher performing cylinder heads that don't need as much overlap, the correct camshaft for a lot of applications will be 113-114-115 LSA.  On some factory headed applications, I'll either be on the higher side of 110 for some mild applications, or to make the old factory iron sit up and talk, I'll be on the lower end (106-107-108-109).  I did two FE's in the past several months that even had 116-117 LSAs. 

I know that I've also said this 16000 times, but you can't count on the "RPM Range" to be anywhere correct.  There are many, many, many variables that play into where a camshaft puts the peaks, including displacement, cylinder head flow, etc.  That camshaft may pull to 6500 in a 352-390, but it wouldn't get within 10 miles of 6500 in something like a 482-496. 

I've seen this happen on extremely rare occasions when a factory block has a big, deep chamfer at the top of the lifter bore.   I use mainly Morel lifters and just don't see many issues on a large sample size. 

I really wish I could get everyone in the habit of priming the oil pump with the intake manifold off, just to see where the oil is going.  95% of issues would be caught, but lots of guys like to put the entire engine together, stick it in the car, then prime the pump.

Most of them are marked L19.  Some of the rod manufacturers private label them, so they may be a little harder to find.