[Thealien]

Tough question and I am not sure it will be easily answered.

What are your planned use of the vehicle? Local? Trips on the highway? Plan on keeping the vehicle forever or selling it?

I swapped a 5.3 LS into a 72 Jimmy about 10 years ago. I went from 10 miles per gallon too close to 20 miles per gallon. I would need to drive about 1,000,000 miles to recoup the cost of the LS swap though.

One of the advantages to me of the LS swap is drivability and easy starts. I could leave that vehicle for six months turn the key and it would fire right up. Adding the Holley fuel injection to the 396 could make that as efficient and as dependable but I have no first-hand experience. I have someone doing an installation on my 1970 to 2 Wheel Dr. Blazer and he loves the Holley fuel injection systems.
I could leave that vehicle for six months turn the key and it would fire right up. Adding the Holley fuel injection to the 396 could make that as efficient and as dependable but I have no first-hand experience. I have someone doing an installation on my 1970 22 Wheel Dr. Blazer and he loves the Holley fuel injection systems.

I am interested to hear some of the other replies.