Engine conversion.

[Pinkbits]

I have a 96 Econovan cab chassis with a 3.1 x 1.8 x 1.8 box van on the back. This morning on the way to work I noticed the temp gauge reading a little higher than normal. When checking the radiator there was no water to be seen, next, I took off the oil filler cap and as I suspected, blown head gasket!.
To make matters worse, I only just replaced the head gasket and re-coed the head 4 months prior.
I am now thinking, as the vehicle is slightly under powered (I usually only carry around 5-6 hundred kilos fully loaded and runs dual fuel with twin tanks) of doing an engine conversion, with the following options.
1. rebuild and turbo existing
2. V6 mazda
3. Telstar factory turbo engine (mid to late 80's)
4. 5ltr efi from E series to AU.
5. Holden V6 conv.
If any one can point me in the right direction as far as conversions that have been carried out, problems, engineering, contacts etc.
Your input would be greatly appreciated.
Thanks, Mark.