They could, and did, carry either. The Mk. 81's are 250 lb, the Mk. 82's are 500 lb.  Six Mk. 82's will fit on a multiple ejector rack (MER), as will, of course, six of the smaller Mk. 81's.

Those look great guys!!! You might want to do a forum search for the old Phantom GBs on the Group Build forum. Here's mine, though she's the Hasegawa kit (Hammer would yell at me) with Zotz decals: 

Old Hasegawa 1/48 F4B

and the old Monogram 1/48 F4C I built back in the 80's and still with me

Just ordered the Academy F4-B which is in the mail.

Very nice builds guys. I'm thinking about getting the Academy 1:48 F4 (Viet Nam)  this year.

Old Revell 1/72 scale F-4B, built 30 some odd years ago as one of the F4H-1F (F-4A) pre-production aircraft

Yes, that is an IDF F-4. I made it in 1973 October War livery as best I could from the little information that I had at that time. I want to try an get Tumbleweed finished this year. I actually have the wings glued on but no photos. My big hang up on the project before I moved early last year was adding detail to the camera bay.

This is the same Revell F-4E kit that Tex built way back when. I built mine in 1991, but it was one of those old kits that I had in my stash from my last "childhood" Christmas in 1982. It is an very basic old kit. I did replace the kit cockpit with one salvaged from a Monogram F-4C/D. I also used the wing tanks, missile pylons & missiles from that kit on this one as well. Decals are from my spares bin and the camo pattern was taken off the instructions for an old 1/72 Airfix kit.

I also have this 1/48 Testors RF-4C in progress that is currently sidelined. I am rescribing and upgrading the kit.

and will be finishing it in Vietnam War markings as this aircraft

Here's mine. All but the RAF bird are 1/72

When I returned to scale modeling, around 1988 or so, I build this Revell F-4E.  It was quite a crappy kit, but I knew very little about it then.  It was the second 1/48 aircraft for me, and the second paint job with my then-new Paasche Model H.  Heck, iifc, I was still using "canned air" for a propellant.   After all those years, I finally made some quick pics at our kitchen table last fall.  I am a bit embarrassed by the ol' girl, but what the hell, I'll play too! 

Gary