I see a lot of problems, but none that can't be solved.
First of all is the heated chamber, not a big problem in itself, but you need pretty good temperature control so you don't have to go overkill on laser power (20w diodes aren't cheap to buy or drive)
But you could maybe mount a co2 laser pointed at the peachy mirrors.. altough I don't know how well that'd go down, peachys' mirrors are plastic covered aren't they?
So you might have to replace them, and then calibrate the magnets for heavier mirrors and then maybe replace the magnets(?)
... maybe just go with a heated chamber with good, accurate control
OK so say you do somewhat like the page suggested, heat the powder to within 5° of it's melting point and go with a 2-3w infrared diode, ofc. you'll have to have a new driver, no problem, in all likelyhood you end up having to use black plastics due to reflection, ok sure, now remember that your box needs a z-axis and as such a way to finely spread new powder ontop of your previous layer ,it's not getting any easier.
IMO Too much work, not enough payoff. With that said though I think it's possible, the hardest part (mirrors) is good to go so if you wanna go for it, go for it! The building and problemsolving is after all the fun part