The only thing is they are damn heavy. The other thing is, due to the fact they are open back, they dont have a huge amount of bass. That suits some types of music well, but you should also try plugging into a 2x12 or 4x12 closed back cab - and if you use the combo speakers AND a closed back cab you get an absolutely massive sound.
Your speakers are celestions, but i dont know for sure what model. My combo was made in 78, and it also has marshall labels on the speakers, and apparently mine are goldbacks. I think the majority of the 70s combos used greenbacks of some variety. If you dont get a defiinite answer here, try asking on the plexi-palace marshall forum - you should definitely find out there.