Have some questions.

You are using the same cam as the factory 340 and 360 4 barrel engines, so I would use those HP numbers as an estimate. The 340 was factored by the NHRA at 300 hp so I would think thats a fair estimate. Either carb would work, but I'd run the 670 unless you plan on a bigger cam down the road. Those heads will easily support more cam, so keep that in mind. That being said, you should have a pretty good running street combo with what you have now.

The factory converter used with that cam had a 2200-2400 rpm stall speed, so I would look for a converter in that range as a minimum, 2800 max.

Flowmasters are LOUD. If you like that sort of thing, great, but there are other mufflers which will flow well and not drive you nuts.

The MSD box does not know what distributor is giving it a signal. A factory dist will do fine. The curve should be similar to what the factory used for that cam or perhaps a bit more aggressive.