I'm pretty sure the socket 478 had dual locking arms sort of similar to that used in AMD.
It does, I have one of those in my backup PC. Although somewhat bulky, I'd say it is my favorite retention mechanism since it is quite simple and leaves very little doubt about whether or not the HSF is securely locked in place. With the push-pins, it is nearly impossible to tell how much net force is being applied.
Well, OP did not specify what his before/after temperatures are so his worse temps may not necessarily be that bad.