Hey dude, u can't run android L preview on galaxy core..android L preview is only for google nexus deviceso.so, don't try things like this.otherwise your phone will be damaged
Bro, first I want to say you thank you
1)I saw your screenshots...there is only one network signal.please edit the system ui to show both sims
2)please give options to select sims on the dropdown menu
3.)is it possible to add theme engine???if ...
Don't try it...
It will certainly hard brick ur core as specs of both phones are different. Hard brick means ur phone will not even switch on, then how can you flash stock firmware.
Press thanks if I helped u.
Sent from my GT-I8262 using XD...