I'll try to go a little more in depth with you. The timing cover requires sealant on the mating surfaces when reinstalled. If you have more sealant in some areas than others, when you tighten down the cover is 'loaded' unevenly and can, indeed, crack. You must be careful to tighten easily and evenly as the cover seats. Also, I used a very small amount of sealant, (read, darn small amount, no more than a film). I have no leaks.
Secondly, you will have to remove heads if the part of the head gasket that extends out over the timing cover gets violated. There should be a thin film of grease applied on this part of head gasket to facilitate separation of cover from gasket.
The rear main seal must be positioned to center with a runout dial gauge. During this centering you need plenty of access (room) and therefore I would recommend pulling engine and transmission. This is very easy. This whole job start to finish can easily be done in a weekend. Go get some railroad ties, take a chain saw and cut them into two foot lengths to prop the car into position. You need an engine puller with a leveling bracket. Have shop evacuate A/C, disconnect battery, undo exhaust, remove transmission connections, remove grounding strap, remove front tire for access to 3 wires on starter, undo O2 sensor, go to front of car and remove condensor, radiator, various engine hookups, fuel lines, hoses and pull it out of there. It really is very simple. Take a digital camera and photograph all hookups marked with different colored tie wraps and you should have no problems.