Paul - there are quite a few imported Cobra's over here now including mine, but you don't tend to see them very often, and there are few magazine articles about cars from the USA. The main problem with buying kit cars from overseas is getting an age related plate, this is a must if you are planning on laying out a large wad of the folding stuff.
American Engines and transmissions are not a problem, you can get good advice about different combinations from websites like this before you buy, and technical tips during the build up.
The way I look at it is we are now in a world market and you buy from whoever has the cars or parts that fit the bill. And if you really want a high rise side oiler then thats what you should aim for. The worst thing that you can do is to buy second best and then lust after something else.
Andy