how difficult is it tp replace the timing cover gasket,oil pan gasket and the valve cover gasket? Would like to do some of the work myself and not pay a crap load of labour at a garage.
The timing cover gasket and valve cover gaskets would be easy. Anytime you change the timing cover gasket make sure you change your oil as antifreeze will make it's way into your oil pan. Just keep everything clean and take your time. The oil pan gasket, however, won't. I've heard it's possible to change it with the motor in the car, albeit not without jacking the motor up a few inches, but it would be VERY hard to do with the motor in the car.
I find that changing the oil pan gasket isn't so bad at all. The timing cover gasket is typically more difficult than either of the others you're considering. Remember, for the oil pan gasket, you can simply place the new gasket on top of the oil pan and cinch it back up. You don't have to even raise the engine. I recommend the 1-piece oil pan gaskets made of silicone. All you have to do for them is stretch them around the bottom of the pan and then lay them on top of the pan, and bolt it up. They seal really well, are potentially reusable and long-lasting.
The pain of the timing cover gasket is in replacing the crankshaft seal. It requires removal and replacement of the harmonic damper / pulley combination and therefore a little bit of mechanical skill, plus the aforementioned mixing of oil and antifreeze. Unfortunately, the SBF has a tendency to snap off the longer throughbolts associated with the water pump and timing chain covers, as well. Oxidizing corrosion from the antifreeze often weakens them and the dissimilar metals only worsens the problem. It can get ugly fast.
I don't want you to be intimidated. Just be aware of some of the potential pitfalls. Start with the valve covers, then step up to the timing cover and oil pan. It's never dull, and you're almost guaranteed to learn something about your engine and its operation. Good luck.