Hi Mark, is there much difference in fit and clearance between a Belair 4dr and Convertible? Regarding the clearances you mentioned before my car is an auto and have read post of owners using a smaller starter. Otherwise its the fwd bolt on the L/H upper control arm that is an issue. Apart from these issues stated could you see me being able to obtain the 0.400 inch I'm after?
I am just a Header guy and certainly no expert on these X-Frame cars. The convertible frames have additional reinforcement welded on the bottom of the x frame that is approximately 5/8" thick and runs from the rear wheels forward ending just as the frame begins to curve up in the wheel well area.
This was a problem in the past as Jerry Belanger designed these headers in the late 50's and were never intended for a convertible framed car.
This was one of the major changes that I made when I decided to re-introduce them. I have sold 2 sets to convertible owners and only one has installed them so far. I just spoke with him today and he said they fit well and cleared the frame. I am hoping to get pictures from him in a few days showing the frame clearances and will post them as soon as I can.
As far as the starter goes headers where made to clear the factory starter and have somewhere around 1/4-3/8" clearance there. If you choose to go to an aftermarket gear reduction starter all the better.
Review some of the photos posted as there are several area's that will have much less than 10mm clearance, including port 8 were it turns out of the flange and passes by the frame.
I do not have a car here to confirm much more than has already been said. Some of the other members with a car on hand would likely be more helpful.