No problem. I like the little 307`s. They can be made to run strong and blow a 305`s doors off. Flowmasters and Turbo mufflers are totally different.
Flowmasters have no internal packing, instead they have flow directors. Plates in certain places that create sound deflection. That`s how they get that unique sound. Turbo mufflers are still used today and remain popular. In fact, they are all I use. I use to use flowmasters, but I got mellower as I got older and always loved how deep and mellow Turbo mufflers sound, so I went back to them. Turbo mufflers use a S shape tube inside the muffler, the tube has holes punched in them and they use flow directors per turn. They are packed with fiberglass mating to further dampen the sound.
Me? I would use Turbo mufflers, but that`s just me. As for headers a standard set of 1 5/8 primary size with 3 inch collectors will do you fine.
I would use 2.25 diameter pipe with a X pipe installed to balance the flow and helps the sound. I use to let them exit at the axle without tail pipes or turn downs, with Turbo mufflers the sound is wicked deep. Why it`s louder is because under the vehicle creates a echo chamber. I later ran flowmasters this way and it sounded killer. But when I had to get on the interstate my cruise RPM was 2800 RPM and the constant drone drove me crazy in time so I installed turn downs. If your looking for flowmasters I have a good set for sale on the cheap. If your interested let me know.