It's 3/4" plywood, but there is an additional 1/2" strip around the front making it 1 1/2" thick around the grill cloth. I just (tonight) finished refurbishing my early 2000S cab or I would measure the porting for you. I will measure it the next time I have it open, it's a chore with 43 screws in the back panel! Maybe others would be interested as well if I drew up some plans. Send me or post your email address and I'll send you some pics of it opened up from the back that I took right before I buttoned it up. I do have one of my 200S cabs opened up right now, it's pretty much a miniature 2000S, but I don't know if it's exactly scaled to a 2000S.
As far as MDF.... This sucker weighs a TON in plywood, because of it's weight combined with it's unwieldy size it's a real beast to load and unload. Unless you're an Olympic power lifter, or if it stayed in one place all the time, I think MDF might push it past the point of practicality.
