/// Another Bunch Of 273 Commando Rebuild Questions? ///

Bossanova5 said
1) Piston #8 has a few light scoring marks near the top of the side of the piston. Looks like it might of sucked something in. The cylinder wall shows no damage and neither does the valves.
What do you think this is from?

if no damage anywhere else, i'd guess carbon build up that broke off and rattled around in there. dress the rough spots and ship it.

2) I have been using the Berryman gallon carburetor cleaner dip to clean the pistons. It works ok, but not too the cleanliness that I'm looking for.
Any better ideas to clean the pistons?

media blast, but that's a dangerous game. maybe an ultrasonic cleaner with an aggressive cleaner but tough to do with aluminum.

3) I initially thought that the inside of the block and heads had a lot of grime. But it appears that the castings on everything from the heads, block lifters etc. are really rough and look like grime. I posted below a picture of the inside of two lifters, one cleaned and one dirty. The casting marks a really rough as well.
Is this pretty common?

yeah, looks normal.

4) The firewall side of the intake manifold's sealing edge almost looks like the casting broke off.
Is this lack of the metal surface being present going to be a sealing issue?

it's not broke. sometimes they just look like that from the molds. it'll seal up fine there's plenty of meat.

ETA: if you're just doing a hone/re-ring/bearings & reseal on the motor, i think that piston looks plenty clean.