You may be able to slide the seat back more, no way of telling where it was postioned when you tried the fit. Having you thighs touch the steering wheel isn't that unusual in most British sports cars, most used pretty large diameter wheels and changing to a smaller diameter custom wheel is a popular accessory option. (a quick glance at the accessories section of the Moss catalog will show that) http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=35374
Your ability to fit into most sports cars will depend more on your proportion of leg length to torso length. I'm 6'4" and weigh around 230 and drive a MG Midget so you should be able to fit in the TR6 pretty well with a smaller diameter steering wheel. You just have to try. These are fairly small cars, so don't expect the same level of comfort as you get in a larger sedan though.
'73 Midget (V6)
'59 MGA (I6) under construction
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