bellhousing pan

I am using the std. manual trans bellhousing cast 528820 and having a devil of a time finding the lower inspection cover. I just bought another cover that is very close. There are 6 attaching holes in the base of the housing and the pan should be 6 5/8 by 17.  The latest pan fits 5 of the holes but is only about 6 inches and will not cover the opening completely. The parts book says 1955-1960 all. I guess I would like to know what this current pan fits and if anyone knows where to find the correct pan.
By the way, the parts book calls for bellhousing 1958-60 as 530661. My housing is cast 528820 which I was told is the 530661. Can someone confirm this? My BW T10 bolts up to it fine.

Do you have any pictures of the bellhousing?

I'm using a GMC bellhousing from a big 1959 GMC. I couldnt find the 58-60 bellhousing. I had a custom clutch made for that big gmc flywheel. Years later I found the correct bellhousing and when I went to swap bellhousings the smaller pontiac bellhousing didnt clear the flywheel.

I know i had an inspection cover for at least one of the bellhousings. Let me see what I have. If I dont have one then you may never find one. I had my entire muncie swap done on my car 3 years before I found a set of pedals.