What do you think it will make?

Depending on your gears and converter, I would consider a 750 cfm carb, but the 670 will be fine for the street. Speaking of converters, spend the cash for a good quality unit. Also, don't overlook the small things like a 3/8 fuel line and pickup tube in the tank. If you pay close attention to the details like that, you could probably beat the 400 mark by a fair margin. There are much better flowing and sounding mufflers than the 40 FM as well (you make like their sound, to each his own).

As for weight, the 340 and 360 will weigh about the same, although a 340 had heavier pistons and the 340 steel crank is heavier. Depending on how your Dart is equipped and the year, I would guess 3200-3500#. The post 73 cars really packed on some pounds, especially with PS, PB, and A/C.