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Yoop.
Off topic here but what did the bbk kit come up with as far as a squish clearance?
Would imagine all these cylinders stock or bbk have different heights.

The weak link on any valve is were the Stem meets the head.
I would think if it got that hot to break the stem mid way up, the temper was also taken out of the piston.
I'm thinking these lame break in procedures for stock or bbk is due to Dino rings and not a final finish with a Plateau hone of 400-600 grit.
A much better ring seal can be created with a good set of modern rings and the Plateau hone preferably with torque plates.
then you can break it in like you stole it.
btw yoop very nice carb set-up!!

Dug deep into my archives and resources.
Top of pin bore to timing edge. .491 or 12.47mm
Compression distance or Compression height=center of pin bore to timing edge of piston. .78622 or 19.97mm
Valve angle 21 degrees.
Made some special for a customer several years ago.
57.5mm bore with a .044 dome rise=11.1-1 compression ratio.
15mm taper wall pin weight=35.5 grams.
Nice ring pckg. 1.mm or .039 top ring Alloy Steel Ferrox coated Chrome Faced, Second ring 1.2mm or .047 Cast iron Phosphate coated taper ring. Oil ring low tension 2.5mm or .098 Stainless spacer with Chrome faced rails.
Thinking of making a dozen of these in 59mm bore.
Piston weight would be in the 109.1 gram area.
Bore out stock cast iron sleeve and replace with Forged Aluminum and have Millennium plate it. I can run a much tighter piston to cylinder clearance this way.
The best place for Cast Iron is on the back yard grill
Cast iron has terrible heat dissipation and Thermal expansion qualities.

Do they bust the valve head off or blow the keepers out of the retainer?

Anyone have cam specs for some of these aftermarket Hot Rod cams?
I'm looking for specs. on lift,duration and lobe separation.
all I have found has been. this or that cam makes better mid to low end or mid to high end.
Thanks in advance.

You do not measure to the top of the dome.
Think in terms of a two stroke. This would be to the timing edge.
A crank with a longer rod only effects the Rod to Stroke ratio not the displacement. This would also mandate a change in wrist pin location.
Longer rod= shorter piston, Short rod=long/tall piston.
A longer rod in a engine straitens out harsh rod angles, Longer piston dwell time at TDC and BDC, easier on cylinder walls, Piston skirts.
Helps keep the rings more square to the bore once the piston changes direction.
For instance a SBC with 3.480 stroke and stock 5.7 rod has a stock pin height of 1.550 with a 9.025 deck height
A SBC with a 3.480 stroke with a 6.125 rod has a 1.125 pin height.
No change in displacement.
Can someone measure me a piston Please
Thanks in advance.