Heatsinks are a problem. The big ones are hard to find and expensive. The best bet is to try junkyards and surplus places. I ended up going with water-cooling, but that's not for everyone.
Changing the value of the resistors will change the operating point for the output devices. Within limits, you can fiddle with the values, but I'd recommend staying with the published values until you've got a good grasp of what the circuit is doing and why. If you want to modify it later, you can do so.
While I'm wainting for the part to arrive I found out a 24V 60W light bulb (that looks like an ordinary lightbulb). I don't know wath is the purpose of this lamp, since here in Portugal we use 220V... perhaps boats???
Well, after some measurements, V=2.6134*R-6.4318 is the equation of the tension funtion of resistence. 12V => 7.05 ohms
Now to see if they work I just need to see what will be the tension in these bulbs. I will use a 25-0-25 transformer.
If someone has built one with this transformer, share some info pleeeeeease!