Alastair,
I have found it very easy to deal with US salesmen as long as you have done your homework. I was recommended to speak with Ron at Ron Campbell Ford who are Saleen dealers. He was very approachable and seems genuinely interested in the cars he sells.
I have eventually done a deal with him on their demonstrator.
SVA as ninja says is really up to what you want to live with. There are a few companies who can mod the rear lights as standard or some that just bodge. the best advice here is to go onto some Uk sites for American motors and ask around. I tried
www.rebel-v8.com and also the ACCI site.
If you want to ship yourself I would advise using a decent agent such as Rybec or Golden Chariots as they have imported loads of cars and trucks with no hassle.
Also, dont rule out UK dealers as they too can be hammered down on price. I have gone through 51st State Autos and the deal I have is only slightly more expensive than doing it myself but I have the assurance of having some warranty and service backup if things go wrong.
Kev