Brent at PML would like to know if the outter most turned down lip on the gasket flange is needed for proper sealing(gasket retention or just rigidity) any input would be helpful. the new cover would be a thick wall AL and have a heavy flange for sealing.

As far as moving the walls on the slant 6 valve cover outward all the way to be flush with the flange

I'm just trying to understand what the design constraints are for a new cover. The finished design may have an external flange like the stock cover (certainly would if there is something non flexible running right up against the side of the valve cover) or it might be similar to our 7872 valve covers. Not being familiar with the ins and outs of the slant 6 engine and it's plumbing/wiring etc, I'm relying on you to give us the information needed.[/quote[

If I were closer, I'd show up in person to help out. One thing that's important is to measure the height of rear area of the stock valve cover. Notice how it's lower in height at the rear -- this is intentional, for some applications have very tight clearance in the engine bay in that area. At the same time, it's important to maintain sufficient internal height clearance for whatever stock or modified cam/rocker setups people might be running.

Have we already discussed the need for baffles and holes?