To answer a question, the grill material is real Marshall Cane as per the vintage guitar amps. Its really expensive at $53 for piece thats 31" X 36" (enough to do both speakers). This material is very stiff and must first be glued to the front of the grill with contact cement and then the corners need to be ironed over the back side with an iron set on high. In case you don't know, heat is a great activator for contact cement and will make it stick like the proverbial *** to a blanket.
You can get Marshall Cane and lots of other vintage grill cloth on the net from a few sources, but the best I've found is a company called Mojo Musical Supply out of Burgaw, North Carolina. Their website is mojotone.com and they give great service and have the best prices.
Good luck with your own upgrades.
Fasted