The list of things that can cause oil burning is lengthy. I agree with Doug to assume its an easy one unless testing proves otherwise.
If this were 40 years ago & the engine was "stock", it would be a no-brainer ... the rod bearings would be shot & throwing excessive oil on the cylinder walls. The second tell-tale of this would be low oil pressure, due to the excessive clearances of the damaged rod bearings. I'd like to mention that your Pantera's rod bearings sound like they are in good shape, and by your description I'd say the engine has tappet bore bushings installed.
My suggestion for proceeding is to have a leak-down test performed, its more informative than a compression test, and it will establish if there is a problem with the rings, or if any particular cylinder stands-out as a problem.
It is true some mechanics like to leave the valve guide seals off, mostly to promote better lubrication of the exhaust guides. The exhaust ports can behave like venturis and suck oil right out of the valve covers and into the exhaust system. This is downstream of the combustion chamber, so the engine can pass a leak-down test, and the plugs can be clean, and this can still cause oil consumption (but technically its not oil burning). If this were the case you should find oil particles on the rear of the car after a drive. Removal of one valve cover and a visual inspection can answer the question of whether or not the seals were installed.
The rest of this is conjecture, just rattling-off possibilities that come to mind, things that other folks haven't already mentioned:
- The pedestals for half of the rocker arms are located right on top of the intake ports. The casting between the bottom of the threaded rocker arm boss and the intake port is rather thin. When some guys machine & tap the rocker pedestals for adjustable rocker arms, they use a "pointed" tap to re-tap the stud bosses, and that pointed tap pokes holes in the roof of the intake port. That hole will allow the intake system to suck a lot of oil right past the threads of the rocker studs.
- Installing the second ring upside-down (aka the Napier ring) will cause extreme oil burning.
- Excessive connecting rod "side clearance" will throw an excessive amount of oil on the cylinder walls. Many mechanics ignore the side clearance spec because they don't understand what it is for. Camshafts and cylinder walls are "splash" lubricated ... the rod side clearance is where that "splash" comes from. It should never exceed 0.020". What this would indicate is that the manufacturer of the stroker crank machined the rod journals too wide.
- One of the symptoms of an improperly balanced reciprocating assembly is piston ring problems, and of course the usual symptom of a piston ring issue is oil burning.
Good luck, lets hope its something easy to fix, like a pcv valve.