A valve guide keeps the valve straight.

Valve keepers keep the valve secured.

Right handed batters were predominant in those days, and their batting stance transitions more smoothly into the run to where first base currently sits.

With only that info it could be,

1970, 350ci, 255 HP, 4 bbls, K10 & K20, C10 to 3500, standard 3 spd or a/t,

or

1979, 350ci, 165 HP, 4 bbls, C10 to 2500, conv. cab, manual trans, fed.

YES NO problems

By watching it rotate and counting

I'm assuming you are talking about rocker arm studs. The only problem with them as opposed to screw in studs is they can pull out of the head when high pressure valve springs are used (to accommodate high lift camshafts.)

Roughly 550 pounds dry.

All other things equal, yes. For several reasons. The biggest one is the extra 45 CID the 350 has. A 305 is basically an underbored 350 and was designed as an economy engine. The small bore of the 305 limits the valve sizes that can be used because of clearance problems with the block itself. If you want to go fast, the 305 is one of the worst small block Chevy engines you can build. Only the 262 and 267 are even worse when it comes to performance potential.

Casting numbers on top of the bellhousing flange and the suffix number on the block deck in front of the passenger side head. The casting numbers will tell you which block casting you have. The suffix will tell you what HP rating it had, what it was likely installed in, and what transmission was mated to it.

Yes. They are identical because externally the 350 and 400 are also identical.

What year and size engine has casting number B1378704E