Is there a Rev CopyBits equivalent?

[TJ Frame]

Been doing some game related coding recently and I'm curious to know if
there is a practical way to perform a blit procedure in rev
simialr to that old quickdraw cornerstone : CopyBits
 Say for example you have 2 windows, the main screen window and an invisible
"scratch" window. I would like to be able to write:
 CopyBits the pixMapID of stack "scratchWin", the pixMapID of stack
"mainWin", copyRect, destRect,"srcopy", the short id of image "maskImage"
 Would an external be need for such a thing? If so, would the callback
overhead nullify any speed advantage of using an external to the point where
its not really practical to use?
 - TJ