Like many others, I want to replace the gate valves on my washer
supply lines with proper ball valves. I'm comfortable with sweating
copper pipes where I have good access, which I do not have in this
case. So what I'd like to do if possible is put a ball valve directly
on the outlet of each existing gate valve, and then attach my supply
hoses to the ball valve outlets respectively - all using threaded
components.

I realize this will involve a variety of adapters and fittings, if
it's even possible at all. Can someone privy to plumbing terminology
help me come up with a bill of materials to hand to the local parts
counter? Or are there compelling reasons not to do it this way?

Thanks!
dakota2112