Stock 340 intakes

How good are those old cast iron 340 intakes. I have a 1969 one in great shape but never used it. Its so heavy but cheap-since I already have it.

Right now am using a Holley Street Dominator intake. Motor runs fine at all speeds but thought a dual plane intake may help my gas mileage a bit. Rest of my combo is not for mileage so not looking for a lot but 1 or 2 MPG would help out.

Was also looking at the RPM and Weiand Stealth but those are over $200 but are light weight, the old LD 340 go for $150+ now on E-bay, thats too much for a 40 year old intake which the Stealth looks like for just $50 more-E-bay shipping fees are higher than Summit.