AS for the conversion....
there isn't much info out there (yer i know someone will correct me..and i hope they do)on the web as to manufacturer and componant choices.
My old mans 351 has an Impco 300A converter (too small), a holley 600cfm baseplate an adapater and a 425 horn mixer placed on top and upside down.
Works pretty good, but runs out of gas at higher RPM.
I'd reccomend it.
the biggest issue was bonnet clearance...remove insulation, and we had to shave some of the baseplate and the adapter.
The adapter is available off the shelf.
If you go straight gas, then don't muck with a regular carby, either use something like this, or a straight gas carby.. Sprint gas make some interesting items, like seperate twin throats that look really cool.
Given you have a ute, a dual bottle setup would be desirable...similar to my old mans ute. We have an under tray bottle and an inside tray bottle. Ok the inside bottle is about 80 litres, but theres nothing to say one of the bottles cannot be smaller..as a reserve if you like.
See pic below.