These were opened up to match the 2GC carb, didn't idle very well, but acceloration from 2500 up was notedly improved.
Running a car under these conditions was difficult, because: If you broke the rules you could loos your number and couldn't race anymore. The only engine change they made all the while I was there was the cylinder heads, Cheater heads were available, so running aftermarket heads became legal .
The last couple a years everything was leagle except the engine mods, because they were discontinuing the flathead in faver of a 310ci OHV engine, we could bore the flathead .020" over the 3 5/16 to save a block. nice of them.
Two year later they turned it into a shopping male, the end of an era!!