Need Help Identifing Small Block Cylinder Heads

Hello, I have a set of High Performance Cylinder Heads off an older Chevy 350 engine. On the side of the heads near the bottom says Bill Mitchell and there is a stamping that has the numbers 378. On the heads their is the numbers 11 21 between the springs. They are angle plug heads. Any other info would be great.[IMG]http://i106.photobucket.com/albums/m.../headspic5.jpg[/IMG]

[IMG]http://i106.photobucket.com/albums/m.../headspic4.jpg[/IMG]

[IMG]http://i106.photobucket.com/albums/m.../HeadsPic3.jpg[/IMG]

[IMG]http://i106.photobucket.com/albums/m...e/headpic1.jpg[/IMG]

[IMG]http://i106.photobucket.com/albums/m.../Headspic2.jpg[/IMG]

Welcome to CHR!

Bill Mitchell Products - they look to me like World Products Sportsman II cast iron heads (big valves). If they have no cracks, these should be decent head for mild to mid-level build. Probably worth 50 horse over stock.