Rusty- the head mounting flange on the header is opened up to a 340-360 port and the factory 273 port is smaller. I cannot show a picture right now but the compressed gasket instead of like 1/4” flange surface is cut down to less than 1/8” due to the size difference. The d-450 headers port sizes are larger than the 273 flange surface so gasket compression is very narrow and I can see issue with leaks down the road. I’ve looked for a all copper or aluminum plate gasket cut for the 273-318 head without air ports would help but welding the flange smaller and machining them flat is the real fix.... or wait 4-5 more months for another set.