'92 Ford Laser GL help installing sound system

[helms]

hey guys, mums given me her ford laser and i want to go about installing speakers and a head unit. however i'm not sure of what dimensions they are. i'd also be keen in putting in rear speakers however the '92 laser hatch back doesnt have rear speakers. also the car doesnt have a divider between the rear seats and the boot any more so i cant mount speakers in that so i was thinking i might have to build a box to hold the speakers and mount them in the actual boot.. (dunno how else to explain that hope some one understands what i mean)

in other words i really just need some help with dimensions for front speakers and head unit also any tips or suggestions couldnt hurt, or else can some one point me in the direction of where to go for help. cheers michael