You have plenty of Cam,and use the 770...its way better to lean out a bigger carb than richen up a small one. My '72 Demon had a stock bottom end 360 w/MP .484/284 Cam,Holley strip dom intake,and Holley 750,3800 stall, 4:56 gear,SS springs,9x28 slicks and ran a best of 12.28 @ 108 mph. Now I did race it every weekend,so I had a lot of time to fine tune it.
Sounds like you want to be a little more streetable,so don't go crazy with the gear,3:91 sounds good,and don't be afraid to run SS springs on the street,they'll be just fine. You should be able to dip into the 12's no problem!
I don't like the way your machinist sounds,you're paying him good money for hopefully a good finished product,Don't be afraid to get info out of him.
I hope it all turns out well in the end!!
Best of luck!!
Wally.