U ROCK,
A Dremel is a rather slow piece of equipment. A heavy duty die grinder, air or electric, will drive a large rotary rasp or carbide burr for very fast material removal, especially in aluminum. A ball and a cone shaped burr, some medium grinding burrs, sanding cones, safety glasses, and disposable dust masks would be a good start. You'll also need a good means of holding the manifold in position to perform the work. A large vise on a sturdy bench works well. You can cradle the manifold in an old towel to prevent the vise from marring the finish and lightly squeeze it in position. One of those portable workbench/vise combinations might also work, like that Black & Decker WorkMate thingy.
Use the new gasket as a template to scribe marks on the faces of the manifold and head port openings. If you're only matching the manifold to the existing head openings, make a heavy paper or card stock template. Mark the openings with layout die or a permanent marker, then use a sharp scribe to mark the gasket or template sizes.
Cover everything in your work area that you don't want grinding dust to enter, including your vehicle and engine. Chuck a burr in the grinder and machine the ports close to the markings, within about 1/16" (1.5mm). Try to blend the new opening size smoothly back into the manifold passages to a depth of a couple of inches if you can. A gentle transition from the passage to the port is the goal. Try not to alter the area around the injector opening if possible, and pay close attention to the areas you are grinding. You really don't want to break through the casting to a cooling passage, the outside, or the idle air or EGR passages. This would require a trip to your local aluminum welder and would only cost you more time and money.
When you're satisfied with the overall shape and size, make card stock gauges that fit inside the openings. These gauges will make it easier to make all the port openings the same shape and size. For the ports that are "backwards", just fold the gauges the opposite direction.
When all the openings are machined, change to a grinding burr to finish the openings to fit the scribe markings exactly. Finish all the openings with a shop roll or sanding cone to obtain a fairly smooth surface finish. It isn't necessary to get a mirror finish in the port rummers. The only place a high polish is necessary is in the chambers and exhaust ports. Mirror polish isn't benficial in intake systems, and can actually be a bit detrimental. A little turbulence around the walls of the runners can make air flow at the shape transitions a little smoother, and help keep fuel atomized as it mixes into the chambers. Double check all the port opening sizes with a caliper (or at least a steel scale) to make sure they are close to the right sizes.
When all material removal is complete, wash the entire maniford thoroughly in hot soapy water and rinse. A utility sink with a hose works well for this. Dry it thoroughly and start assembling. The whole process shouldn't take more than a long day if you're only matching the intake to the heads. I'd guess about four-five solid hours on the porting the intake on both sets of openings.
Don't forget to apply anti-seize to all the fasteners when they are installed.
If you want to port the plenum and runners, this would be a good time. Check this article:
Plenum Porting.pdf
This should take another five-six hours, but might be a little less if you're already set up to cut aluminum.
When you're all finished, you should have another 10-12 horsepower at your disposal. Some say the plenum porting alone is worth 15 HP, but I'd think that is a bit optomistic. At least a 10HP gain is almost assured.
Once that's all done, you can imagine how much power the boys in the bow ties left to get out of the heads with a little grinding.
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Later,
Vader
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"
No matter how hard you try you can't stop us now"
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