*updated reply*
I mean, if you think about it like this...the power you would be getting out of it would be too raw than refined...why would you want raw power over refined? It's like buying the cheap bottle of clear whiskey when you could buy the premium aged whiskey for more, it all does the same job but effects you differently and goes down a whole lot easier vs harsher.
If you did get 2 processor's onto it (and you CAN, it's just stupid and nearly impossible unless done 101% right and you need to be thinking out of the "box")
With 2 processors soldered together you need to think of it as a reverse domino effect...
Sure, you'll get a increase in power but it could result to way more negatives than pro's, mainly because you're not getting the "hemi-effect" of actual duo-core processors now.
I mean unless you have a 800mhz+ processor sitting in that g3 it's really not worth it.
The "hemi" effect that I am talking about has to do with processors activating and de-activating. It's like this, you have program A using X amount of processing power and program B using X amount of processing power with Y amount of ram, the processor is unable to differentiate the difference between a(x) and b(x) there for causing a unstable environment for the CPU and it's unable to correctly process as a "dual" core processor but instead is acting like a single core in which all programs are feeding off of a single CPU and not two as intended. It goes back to what I said, it goes to raw power VS refined power, a GPU upgrade as well as a RAM upgrade would be much much much more significant. That and the capacitors on your mother board would not be able to handle the additional data flow without additional upgrades. The bottom line is, it's smarter just getting a new motherboard that is intel based and putting a old OS on there and stuffing everything into that G3. If your G3 is a tower that should be very easy.
But if it's the iMac model like I have, then it might be tricky. There are a lot of variabls that go into play here and I could talk for forever and I'd be happy to chat with anyone that knows what they're talking about as well to debate facts over "this might work" to compare and to even help out as much as I can the making this work, but the only thing I ask is to make a youtube video for us to watch the progress of the work and to see the final product inside the computer and then it working, you should do a before and after.
p.s. for the love of god, buy a HUGE heatsink and fan to put on that thing if you do it as well!!!!!!!!!!!!!!!!!!!!!!😱