Large valved 273

The biggest things about notching the bore are keeping the notch inside the gasket sealing ring, and making sure the top ring doesn't get in to the notch. IOW's, don't get the notch too far down or the rings too far up that the notch and the rings run into each other.

I haven't done it in years, because with aftermarket blocks and such there isn't really a need for it. But I used to do a ton of BBC stuff and have done 3 273's that I remember.

I can tell you in the early 1980's those 273's made a butt load of cash on the street. I've seen damn near full scale brawls break out over guys getting beat and then saying they weren't 273's. Many times guys had to crawl under the cars to verify the casting numbers on the blocks.

Solid lifters, big valve heads and 4.56 gears made many guys pay through the nose.