The new seats came with the 4.2 in late '64 and yes they are better. The 4.2 also got better brakes (still not brilliant, but better than the 3.8's), Jaguar's own all-syncro gearbox, alternator / negative earth electrics, and a few other minor improvements. I had a 4.2 OTS for 14 years. Now I have a 3.8 FHC - read what like into that!
I love the 3.8FHC, heres a pic of my old one. I prefer it over the 4.2 but I just can't do the seats LOL Image Unavailable, Please Login
I have a '66 4.2 coupe - it's a driver. Not necessarily for sale, but who knows? What is your budget?
I'd love a '65-'67 SI FHC. Have even considered selling "Old Blue" (avatar pic) for one. A respectable driver, nice, not perfect, not a show car. Solid, reliable. Someday perhaps....