Hi there.. two questions...

1. What exactly are the differences between a Type 1 exhuast and a Type 3 exhuast?

2. To replace shock absorbers, all you have to do is take the weight of the suspension (jack up the car) and undo the bolts, and swap over, right? Is there any little points to remember? Tips?

Thanks in advance!

1.
a) You can still buy original type 1 exhausts without mortgaging your house.
b) Mufflers are different
c) Type 1 have two tail pipes, type 3 have one

2.Right. That's about all there is to it.
Use axle stands as you will probably have to get under the car.
Use new bolts.
Use never seize on the bolts.

1.
Further to what Purple said, if it's a stock exhaust there are also a few differences with the heat exchangers, particularly where exhaust comes out at cylinder 2 and 4.