don't get the new haynes book of lies, try to find an older one as that has a lot more detail in it, instead of telling you to just buy a new part. i also have an autodata one from the early 80's for the MK1 which has alot of info on getting the car to run properly. carb is easy to change if you know how, just remember you will need a new gasket.
they all came with unpainted body kits, painted ones were dealer special's to shift excess stock.
flush the block out aswell. also check the water pump.
what you need is a big breaker bar, a hammer and someone to help.
put your locking key on, put breaker bar and socket on, then put some pressure on the breaker bar as to undo it, make sure you hold it square, then get someone to hit the breaker bar with a hammer, make sure its a decent sized one. normally works.