hi mate,
If you seach, or even srcoll though the pages of this section, there are heaps of threads on TB42 turbos.
The answer you will get to you situation is to go straight gas, get rid of the carby.
Fit a gas research carby/throttle body and a gas research B2 converter.
I have been looking at these options for ages - and this is pretty much THE setup. There are a few variations... but this is the most common path.
Setting the carby up for forced induction would be difficult and probably expensive - and then you would run on gas 95+% of the time any way.
Converting to injection will cost too - then you need to be able to map it to suit boost - and then you will run on gas 95+% of the time still.
You will need some ignition control, but these are available - and much cheaper than an aftermarket computer that would be required to run petrol set up.
I have an efi tb42 that i am planning on turboing - when i get time. I am considering trying to leave the factory injection in place for the easy start up, and hoping it would still drive under very conservative boost on petrol to get me out of trouble if i needed it. But it will probably end up straight gas too...
Good luck with it.
Cheers
Stew