I think the 142 Main would be a good starting point. Im thinking its going to be perfect or you will have to drop it down one size on the main. Try it out...see how it runs. You can always use choke to determine if its running lean or rich. If its running like crap and you pull the choke out and it runs better than your lean. If its running like crap and you pull the choke out and it dies then most likely your rich. Try it out and report back.
I may be totally off here since you do not have a snorkel or pipe (i usually assume someone already has those mods) but starting with a big main is better than a small main. Good luck!