BLOCKING OFF HEAT RISER
 

Do the flow advantages in blocking off the heat risers in the head justify the work involved?

yes

not a flow advantage, but a heat issue with the fuel in the carb.

Yes, a flow advantage on the 4 EXH bowls.
Yes, a reversion-contamination isolation-advantage on 4 & 3 vs 6 & 5.
Yes, a cooler head temperature...in the middle-zone where the fastner shank show surface rust.
Yes, a cooler head temperature...in the middle-zone where the head-gasket shown plastic deformation reflow...and likes to blow.

I think it'sa good idea to Fill our crossovers, rather than blocking plates or leave open.

Consider it a std op for headers.

Not just with headers- as HIS pointed out, 'sharing' of exhaust ports by cylinders 1/3 & 2/4 ain't good- reversion, etc.

Not worth half the effort on a street car unless already doing a major overhaul on the heads.
If race only then yes.

I'd have to go along with BVR421 with a big "it depends."

What exactly are you trying to accomplish with the engine? If it's simply a strong street engine in a cruiser, then I don't see it as being worth the effort.

If you're setting the car up for maximum performance, whether street or strip, then yes, it's definitely worth the effort.

explain flow advantage? a reversion-contamination isolation-advantage on 4 & 3 vs 6 & 5.
if order is 1 8 4 3 6 5 7 2, and 4 6 are common with 3 5 common, how can the exhaust from opposite cylinders interfere? There is no back pressure from one on the other?