Not So Tiny Bubble,
Since I have roughly the same height and weight numbers you have I hope I can be of some help here.
When I decided to purchase a Cobra I looked into the used market and really found that whatever I sat in did not work for me. The best place to do this I found was House of CObras in Ca. because they had all sorts of different brands to sit in at one location.
After further working with manufacturers I found that most would be able to accomodate with either different footboxes, lowered seat deck, removed chair rails, and/or reduced cushioning in the actual seat. (or combination of them all).
You will find that while you are big, that most cars can be built to accept your size.
Some advice:
Buy new instead of used -- you may get lucky in the used market but I found it more difficult.
Talk to each manufacturer to see what they can do.
ERA, Superformance, Unique, FF5 all (I believe may be able to accomodate)
Don't get bigger or better yet get smaller like I am trying to do.
Good luck in your search