My fixie frame with the 75mm stem is circa 1968-1970 (Marco you'd be proud
) so has steel forks with the more old fashioned curlier rake. I wouldn't want to race on it like this, but for general riding / TTing it's fine, not overly twitchy. You can still ride no hands on a reasonable road surface for example.
Re the layback seatpost I think most main manufacturers do a staight and layback version. The one I have (again on the fixie - it was a budget build up) is a basic Alu one from Evans (Selcof "Team" I think) and only cost about £15. I think Selcof do some reasonable budget posts.
I had a Selcof post in my older bike originally which had a bit of layback on it, I'll have a route around the garage and see if I've still got it. Being short of leg it isn't very long but it might do. I'm guessing your frame will be a standard diamond frame anyway so won't have any of this more modern long exposed seatpost malarkey.