Personally I recommend you take it to the shop and have it done right. If you have to do it yourself I would recommend pulling the hub assembly complete and putting it on the bench where you can drill/grind out the bolt heads and slide the assembly apart. Once apart you can throw the offend hub in the trash. If you had've purchased a factory Volvo hub/bearing assembly it would've come with brand new shiney bolts, but oh well. The SKF assembly is the same thing only it comes with no bolts and costs a whole bunch less. I would put it back together with factory, torx head bolts and use a little anti-sleeze when you do.
On the "need a puller for the ball joint" idea, it is not necessary if you use the correct technique. Hit it with some penetrant and get under that sucker and give it a quick, straight, pull down and out. You have you give it a might yank and if you are laying on your back it might be a little on the tough side but trying to pry it out with a big screwdriver is pretty much an excercise in futility. Often times on the first yank it will only come out about half way and stick, in case this happens just spray some more lube on it, tap it back in with a hammer, and give it another might yank straight down, repeat as many times as necessary, usually 2-3 times on a tough one.

Mark