OK,
First off I want to say to Mike... Nice intake, I'd bolt that on anyday! IMO the method you mentioned is probably the most practical when you factor in time, money and end result. I agree that it's a nice effective way to adapt the intake.
The following is just my :2cents: explaining my choice.
I chose to do the spacers, but I didn't like the idea of double gaskets. As I mentioned earlier, I am going above and beyond to do it as best I can for one simple reason... I am basically relying on the piston to draw the air into the cylinder. I don't have anything forcing it in so I need the most accurate alignment possible.
When the intake is matched up with the vortec head the runners are mis-aligned at both TOP and BOTTOM. I did a quick photoshop in attemtp to explain what I mean. I know, it's not to scale and upside down... I just wanted to get the point across. Anyway, the YELLOW areas are the VORTEC PORTS and the GREEN area is the surface of the VORTEC HEAD where it would be positioned if mounted without spacers. I made it faint so you can see the intake runners underneath.
As you can see above, the runners of the intake have poor alignment with the vortec heads. The space at the bottom of each runner in the intake is 3/16" and on the vortec heads it's 5/16" also the runer height is 1 7/8" on the intake and 2 1/8" on the vortec head. The goal for the best alignment is to center the smaller intake runner in the larger vortec runner.
There's more involved here than just covering the exposed area of the port by welding on material to the intake. If you can visualize it, imagine the intake raised up (down in pic) to align the bottom edges of the ports. That also nearly eliminates the gap at the top of the port as well. This reduces the amount of port matching needed and improves overall alignment.
My spacers will be permanently welded to the intake around the outside and around each runner. Once machined down it'll hardly be noticeable. It'll fit onto the block and heads just as it did with the L35's with stock '96+ gaskets.
Well, to sum it all up... I am not trying to say that my method is the best and everyone should do it. It's just that IMO it was the best choice for me and i wanted the best quality work. To me a double gasket would have been a patch, not a fix. It probably doesn't make much difference with forced induction, but I feel it would in my case. I can take criticism well so if anything I said is too far fetched please set me straight.
To those that want to do the vortecs... spacers aren't necessary and probably more trouble than they are worth. I am a little picky I guess and needed a litle more. It comforts me to feel as if I have done a professional job.