I was having a similar issue with my Dart (much slower). When I lifted after the traps she would wander. Not scared for my life wander but definitely got my attention. I solved the issue by lifting more gradually. Good luck...
My Kid got the new fan and shroud mounted on the Dart. The fan was intended for mounting to the outside of the shroud but there was not enough clearance. He modified the design so the fan could be mounted to the shroud from the radiator side. I think it came out good.
I have been running the Speedmaster intake manifold (and heads) on the Dart this year. I made too many changes for the time slips to be useful. My best guess the intake is a rough equivalent to the Performer RPM I replaced. I do however, no longer have issues with fuel boiling in the carb on hot...