> Is it safe to always make a call to ...Long() everytime a call needs to be made to ...Proc()?

I think this is safe. But the better way is to call it only once per each HWnd value, and then use the result every time that HWnd is submitted to the CallWindowProc.

Normally the address for the window procedure for a given HWnd does not change unless you hook it directly, for example by calling the BINDEVENT() or calling the SetWindowLong().