they do. the bottoms sit at an angle and sort of plant you in them, I havent had the stock buckets, but they are firm and pretty solid, more so then any 60's or 70's stock seats I have sat in.
for added bolstering, procar has a "rally" model seat, these seats are what turned me on to procar 10+ years ago, when I was rebuilding my Mustang. My seats were not in bad enough shape to replace so I never got the rallys, maybe some day they will end up in my mustang...
Obviously both seats are also available with headrests...
I like em, and my K5 came with 80's blazer seats so I didnt have anything useful to work with (other than the seat-to-floor brackets, thankfully!)