Ok, I figured it out....
1. Get the Lisle Spill Proof Funnel Set (I picked up at NAPA Auto Parts)
2. Go to walmart, go to the plumbing section, and pick up the Peerless Plumbing Repair Kit B206X
3. In the funnel kit, use adapter and cap set B to work with the Mishimoto Radiator.
4. When you take your Mishimoto radiator cap off, you may notice a spot weld in the fill area. If so, use a dremel on the yellow plastic B adapter and make a divet in it that goes around the weld and allows the adapter to sit flush.
5. Now in the picture below, remove the black rubber gromet that comes with the Lisle adapter B & discard.
6. Now take the pink gromet (The one sized like the one shown in the picture in the middle) found in the plumping kit. Use a razor to cut out the inner diamter. The amount I cut out is shown in the below pic, the one on the bottom of the pic. This will leave you with about 2 rings worth. (The completed useable gromet isnt shown in the pic) Discard the inner part you just cut out (Shown at the bottom of the picture).
7. Put the custom gromet onto the adapter B where the black one used to be.
You will now have a revised adapter that will fit over the spot weld and have a new gasket that will allow you to close the cap and not have it leak either.
Hope this helps everyone out!