I am preparing for a similar swap. I managed to find an R151, which mates nicely to the 3.0 R150 bell, which mates nicely to the 3.4 with a 3.0 throwout bearing. Otherwise, I would have chosen the R150 behind the 3.4 and used a Marlin adapter plate to keep things simple (and move the motor forward a tad, which must be done to clear the firewall and work with the radiator - and as a side benefit *should* provide crossover room behind the heads).
Parenthetically, you have to move the whole drivetrain forward about 3" on the 22RE trucks with this conversion. They look the same as the V6 trucks, but they ain't. Even Mike Caskey was surprised when we measured things up from various start points. Just thought I would make your day with that...
I am torn on exhaust as you are. I am considering what you suggested, grind the welds off the stock 3.4 crossover and reverse it. Mike Caskey warned me that fitting the motor is the highest priority, and that may or may not leave adequate room for the stock crossover, so my second option is as BKG describes: a below-the-drivetrain crossover. Not real thrilled at that but should create no clearance problems if done right.
Mike Caskey crosses over behind the tcase. I don't want to go back that far really. I snagged the cat & front exhaust off the donor to make things easier too. I'd love to pay Mike to do the work, frankly, but he doesn't think he could get it done before Cruise Moab.
Yeah, like I could, on evenings and weekends... HAH!
[edit] had another thought... you could go with Downey headers too, and run duals to the cat. Just a thought. Crossover issue remains. Well, you could just use the stock headers too. Nevermind.
