i'm running a pair on a 440 in my '65 coronet. i use 2" tti headers and the angle plugs fit nicely. i'm using a fel-pro 8519 head gasket and 2021 will be my 7th year without any issue. the heads i have weren't very nice casting wise so i piddled with the ports a little. they bolted up fine but i had to do some rocker geometry change and they need custom push rods. i think the big issue with them is rocker geometry and push rod length. there's no way a stock valve train would have worked with what i have.