That is fairly consistent with what I've seen between those intakes also. The 337 does pretty well considering that it is such a low profile intake. It isn't going to be a high rpm intake on a big motor but it does just fine for this type of application.

Another intake in the mix would be the new Super Victor from Edelbrock. It is a tall intake so it wouldn't fit under your hood but it is a good one to compare to the Indy and 337. On my 505 motor the 337 and Super Victor were dead even.

Is that 1050 QF carb a 4500 style carb? So the 1 inch spacer is a spacer/adapter? For street use a 4150 carb might work better even though you'll give up a little top end power. Just another thing to play with. Looks like Dwayne's carb is putting up good numbers. I'd think that a Holley 1000 HP would work pretty well on that motor.

Edit - I see that the 1050 is in fact a 4150 carb so you should be good to go. A Dominator on an adapter would pick up some power for you if you ever feel the need for more power!