Now not starting

Hi all, i have 1981 1.5 carb engined gls and about a month ago it developed a slight misfire when letting off and accelerating (during gearchange) So i stopped driving it for a while.
About 2 weeks ago i decided to change oil and filter and changed fuel filter, this somehow made it run worse and was undriveable dure to the misfire worsening. I then changed the rotar and am dizzy cap which made it run bloody awesome! Took it for a good half hour drive and then happy with it parked it back up.
I went back to it the other day and now its missing really badly again, so replaced the plugs because they were really black and number 1 was cracked. Didn't make any difference so then changed the coil and distirbutor, now it wont even start!  
Should i try replacing the leads also? Or is there some school boy error i may have made along the way? Please help as the car is up for sale and really want to get it sorted before anyone comes to view it.

take the coil back off and compare it to the old one carefully. in particular check inside the spark plug lead hole, the old mk1 coils differ to the later ones. also make surte its the right one for your injection systerm, points ign coil is different to electric ign ones.  to check what you have, look at the dizzy. if it has a 3 pin plug on it you have electronic ign.

leads also worth replacing just to rule em out