Yes I know this sport is not cheap but.....
I burned 110 Gallons at $3.33 per gallon here in California last weekend in my 33 Scarab AVS with Modded 502 MPI 530 HP a side. I love driving. I was thinking how about an Aluminum LS or small block swap to get the weight down and improve efficiency.

I was wondering how fast the boat would go if I went down to 380hp LS engines vs my present set up and how that would affect fuel burn at cruise of 3400RPM BB vs LS> If there any efficient setups that make sense?

That equation will never work out........like trying to justify buying a 100K Tesla to save $40 a week in gas!

Just as a reference point, 32 Sunsation with 6.2 small blocks (320 HP) would burn a gallon a minute at WFO which was 70+ MPH. If you were building a new boat then it might save you two ways (one on the build, one on the usage). To re-rig your existing boat to save money is never going to work out financially.

My best suggestion is to run your engines at 3,000 rpm and head directly to whatever party cove you have close by and anchor out all day followed by returning to the dock at the same rpm.

I burnt bought the same as you if not a couple gals more with 6.2 MPI's in my 312 Fastech & we anchored for 3-4 hrs Sunday...
We ran bout 6 hrs Saturday pretty easy & 2-2.30 Sunday...

the most efficient way to boat is put $100 worth of gas in some one else's boat. same experience and they are thrilled someone gave them gas money.

other than that, if you are worried about the fuel cost, performance boats are not for you.

^^^ This, ..Like to the 15th power

+1. I can run 200 miles on 110 gallons of gas with the 400s.

I can run 200 miles with 80 gallon tank with my BBC.

You meant BBCs!