Mazda Bravo B2600 Injected 1995 model help.

Okay, I was driving up the range the other day and all of a sudden, BANG!
The radiator blew up, put a big foot long split in the top of it (plastic), water went flying over the bonnet and front window.
The motor is not seized, but will now not run. When it was running as I was pulling over it was rough, really rough. Sounded much like a diesel engine, and also had no power.

Question 1:
I think the radiator blew not because of no water in there and it overheated, but I think the head gasket may have given out and a sudden surge of hot cylinder gas blew the radiator up? What do you think?

Question 2:
Looks like I'm going to need a head shave and new gaskets etc. While I'm at it I'm thinking bigger valves maybe for more power. Has anyone ever done this to this particular engine. And was there a big difference in power etc? Maybe a better cam, as this is a ute(truck) I'd like more power up slightly higher in the rpm range.

Engine is a Mazda G6 (I think) 2.6 petrol injected, year of manufacture in 6/1995. It is an Australian car. There is also the 4G54, which seems to be very popular in the USA.

Peter