Install ROM lumia 630 singel sim for & on lumia 630 dual sim

Maybe it'll work but you'll lose dual sim functions and probably will get you signal problem etc.. You can try but under your own risk they're quite the same device but it's probably they'll differ in bands and those things.. You should have original rom handy so you can recover your phone if something goes wrong
 
I see no reason to do so since a ROM flash isn't going to magically add LTE or make another SIM slot appear.