great guide there Nino.
I was just wondering do you use any heat sink compound between the two bridges and the heat sink?
I always use heat sink compound on any thing that bolts to a heat sink. It may not be necessary here but I thought I would ask. 
 

Yes Andrew, I use heaksink compound wherever a heat sink is used.

I know everyone does it ( including me) but is it really necessary to replace the bridge rectifiers?

You don't have to, but while the board is out of the game, it is best to upgrade the all the parts. Capacitors are usually good for 10 years, BRs should be fine for longer.