You started this thread on the topic of stem seals and said your mechanic felt it was stem seals.  It might be seals, but that's not where the smart money is.  A great stem seal will fail quickly with bad guides.  A really good guide can pretty much function without a seal.  Particularly on the exhaust.  As to what it can be under heavy vacuum if not a valve guide issue?  It could be bad intake gaskets.  It could be a flooded or stuck open PCV.  It could be pulling oil past the rings.

You might also want to take a close look at the rotors for cementite formations.  They are very localized heat spots on the rotor and give the feeling of a warped rotor since the cementite is very hard and abrasive and makes the braking feel like it's being pulsed.  It's very hard to machine away cementite and that could change your solution pathways.

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Amen, and so easy to diagnose, if they don't slide in nicely, stop LOL

I would regard the disassembly to be the tell tale.  If the lifters don't come out easily with just finger pressure, you know you have something you need to address.  Certainly assembly is where attention to detail pays off and a lifter fit problem better be identified and fixed.

I too would just run it at .005.  You would be surprised how lose you can run a piston without any issues.  Just make sure you bevel or smooth the bottom of the bore to make sure no sharp edges in the bore.  Now, knurling was a pretty common practice when I first started working in a shop.  There isn't anything wrong with it as long as the machinist is reasonable about the process.  If you have some OCD working against you, you could knurl that one piston and it would be fine.  Again, it is a legitimate machining operation.  That we generally don't do it these days doesn't mean it is an obsolete practice.  Very few shops do small dollar rebuilds these days.  More bucks in a full on job.  Here's an article to give you some perspective:  https://www.enginebuildermag.com/2017/09/lost-art-knurling-pistons-takes-skill-guts/

Normally, yes.  Like everything else, it depends.  Petrochemicals have a shelf life.  Usually, they use butylated hydroxytoluene (BHT) as a preservative, which gives it years of shelf life in a sealed, light impermeable container.  Stored in a cool place, it is going to be useable.  Heat accelerates decomposition so it would have a shorter shelf life.  Temperature is really the variable here since sunlight can't get through the metal can.  Now, normally you wouldn't use it as a race fuel for a competitive event like where a title was on the line, but racers are always looking for fresh fuel to eliminate that as a variable.  If you want to know for sure, send a note to Sunoco with the particulars and see what they have to say.

Thanks, Mike.  If it were easy, everyone would be doing it.  Just to clarify my memory but I seem to recall that your TP head will fit a 428 bore without modifications.  Are you still moving in that direction?

One of these days, everyone will be over their covid.  People are tired of the excuses.  Businesses that don't live up to customer expectations will be replaced by a business that can.  It's not a useful model anymore to be long on excuses and short on products.  Trick Flow needs to find a foundry...even if it's in Iran, that can make the product.  I fully understand manufacturing is a complex system, but money always lubricates the gears so companies who are not motivated and are eager to say they got that covid monkey on their back need to be replaced by the movers.  I mean Edelbrock too.  It seems all they have in stock is the gift shop merch, and they won't be in business long selling t-shirts and stickers.