What part of the world are you in? Fill in your details. ;p
I'm guessing you're in England.
This site sells exhaust headers for the 33, and they're in europe:
When you get the cambelts changed, make sure the shop fit new belt tensioners at the same time. I had my belts changed but the shop didn't change the tensioners, and I didn't know this was important... until 5 months later when a tensioner disintegrated. The car made unhappy diesel noises for almost a week (which two different mechanics couldn't pick), and then there was violence and destruction. =(
The belt change interval listed in my earlier 33's manual is 36,000 miles / 60,000km (quite frequent!)
I don't think it should cost 500 quid, even with two belts and tensioners - the engine doesn't have to come out of the car or anything drastic.
To make the gearshift feel less vague you can have the bushes in the shift linkage replaced. You will probably find difficulty engaging first, second (graunch!) and reverse gears, but apparently synchros in a 33 gearbox don't last long if you replace them anyway. Some people say a synthetic gearbox oil helps.