i would get the discs all around first. then locate some SE rims, or equivalent with tires before i went ahead and swapped bolt patterns.
Brake Conversion Kits : 1979-1983, Basic Drum to Disk Conversion Kit.
buy the bracket from re-speed.com to swap the discs to the rear and run those in the back and keep your bolt pattern why swap entire rear ends just for brakes?
Wheel Studs, Lug Nuts, Spacers, Valve Stem Caps, Wheel Locks
later down the road just drill the 4x114.3 bolt pattern out and thread in the mazdatrix studs and voila! you now have 4x4.5 rears with studs, and can run a numerous amount of rims.
as far as the front either swap over the entire spindles and struts and be done. not worth the time of taking them all apart and stuff just drop them in, or drill the ones you have now up front and run them now. either way.
theirs a cheap way and a buy all new way. take your pick.