Neil,
I was doing some Mazda rotary work at Drake Engineering back when Gurney was developing the Chevy small block for Indy racing. As I remember "Stump" Davis was doing most of the work there on the engine. He developed the down nozzle injection for the small block. He bored holes in the head from the spark plug side and then they welded solid round rods into the bored hole, then drill and tapped them for injector nozzles and the fuel was squirted almost directly on the back side of the intake valve. With a lot of development and dyno time they were making some very good HP. Stu Van Dyne, who was working at Drake saw the advantage of this and developed it for dirt car engines. I think the first was Jr. Kurtz's dirt champ car, the Plastic Express, which also picked up an impressive amount of HP from the down nozzle modification and went on to win both the 82 and 83 Hoosier 100. Stu also made them work on 410 sprinter motors. Regretfully Ron Shaver picked up the idea and was given the credit for getting down nozzles on sprint cars when actually it was Stu.
Any way do the heads have plugged ports on the spark plug side? As I remember Junior's dirt champ motor, 355 cu.in, iron block, was making about 835 hp at 8500 rpm and that was when most of the other cars where making 750 hp max and not turning over 7500. You may have a real piece of history!
Rex