Nick
It looks like the gain would not be much if any at all.
Lots of work to swap the heads and consider the price of gaskets, oil, oil filter and the like. Even though you found a bargain if it was me I would save a bit more and go with heads that will give a substantial gain.
As for weight savings I can think of eaiser & less costly methods.
I'm not sure but after looking at your combo again you might gain more from a cam rather than a head swap.
Why not call one of those cam gurus and ask them what they think?
Later
Grady