When someone says they have a “12 headed engine” what specifically does that mean?Are the valves on a 12 degree angle from the deck or head? Just something I’ve always wondered. Thanks in advance.

Refers to Brodix -12 heads. They had a progression of heads from -8's on up as technology progressed in the 80's and 90's. -12 heads are a 15 degree valve angle. They also have a 12 x 12 head that is a 12 degree valve angle. They can be had with a variety of spark plug angles and port sizes. I'm sure someone will chime in with more details than I can give.

Stock sbc are 23 degrees meaning the valves are inclined upward from the axis of the cyl bore 23 degrees. So yes a 12 degree head has them angled 12 degrees. Hypothetically if the valves were 0 degree they would be parallel to the bore.
Don't confuse this with brodix's -12 head. Idk why or how they came up with that but they've had -8,-10.11 & 12 among others. I believe the -12 was among their first to deviate from 23 degree and I think they were 15

Whats the advantage of angled valves?.... & please don't just say "better breathing"

" valves are inclined upward from the axis of the cyl bore 23 degrees" Does that mean valve face, or valve stem? I wish there was a picture or diagram.....

Stands the valve up more ( 15* compared to 23*) which gives a straighter "runner" for the air to flow through and helps with air speed I believe. 23* heads have what is known as a short turn radius caused by the angle of the intake runner being laid over more.

I wonder why Chevy didn't design valves like that to begin with?

I believe technology has just evolved. The LS style heads stand the valves up also compared to the old small block chevy heads which were 23*

Technically the stem. The lesser the angle, the straighter the path to the cylinder.

Coming from the stovebolt 6 the 265 was a huge leap forward.