The one I'm interested in is the Holley Projection Dual plane PN 300-66. Will it work with the factory TBI unit on a 91 RS? Are they worth the money($179)? Is the Edelbrock 3704 any better? I'll be doing a 305 to 350 swap soon and I'm considering an upgrade.

 

Six in one hand, half-dozen in the other...

I don't think there's a nickel's worth of difference between them. My advice is to go to ebay and buy the cheapest used aftermarket TBI intake you can find if that is the route you are going.

I think the best intake is to use a carb model with a thin adapter plate. You can find so many more to choose from and then match that to your heads (you're upgrading to TPI or LG4, right?) and cam (you're switching to TPI or LT1, right?) to get you the power you want. You should also strip your 350 down to the block and take it to the machine shop. Most likely your truck block isn't machined for the roller lifters but the block is cast for it. It shouldn't cost that much to have them do that bit of machining and then you can mildly upgrade the cam. You can also re-use your roller lifters from your 305 and save some cash!

Then you're a computer tune away from greatness, although a 350 TBI with a TPI cam doesn't make the ECM too upset.

Don't forget the TPI or Vortec (or Wallbro) fuel pump, too.

I really believe that the TBI specific intakes are tuned to near-stock applications. That's just my two cents...