Consider some budget for balancing all or some parts. Just having the flywheel and clutch done together is useful especially with a B20 as it's reckoned to be a bit less smooth than the B18. A lightened flywheel takes a lot of the smoothness away from low speed driving but a good skim of the working face is sensible even if you aren't going to balance it. Volvo internals were at the time considered pretty well balanced but modern engines are better. Things can be improved but time = money.
Thoughtful reading.
http://vclassics.com/archive/badmotor.htm
http://vclassics.com/mppe1.html
Mitch's comment re flywheel not seen when I posted this. I'll stick to my comment. Agree about the fan.