If I were to go modular, unless I was using the Trick Flow heads and wanting to make a car that has that motor stock, surprise people I would not bother using a 2valve. It just isn't worth all the work. They don't breath enough to make lots of power, take just as long to fab up to get in, and don't look as nice.
I would go with a 4 valve just for the "open hood ohhs and ahhhs." It just looks a brawny motor.
What looks better
But that is just the opinion of one guy. But know I didn't even use the Terminator engine, which is 1000 times more aesthetically pleasing.
Either way, the 4.6 isn't a bad engine I just wouldn't swap a 2v when all the same work, and similar money to get a 4v that runs and breaths like a OHC should.
As for adapting a kit, I don't think I would bother. Everyone seems to have problems when they just use a different K-member on each respective kit, much less a completely different chassis. I have a feeling you would be welding more just to straighten out where the pipes don't clear. If you have the time and patience/skills to do so, I would weld your own, after say trying some shorty headers to get it started easier.