One thing I have figured out though...may be just an isolated happening, but when I keep the art in the original CMYK, I have ended up with mixed results. The one time I changed all the colors to PMS Spot colors, it came out perfect at Kinko's. I dropped the ball on this one by not replacing the CMYK with Spot colors. Oh well live & learn, next time...if there is a next time.)
You know as well as I do that there's gonna be a next time, and probably a third and fourth time

I think that was the reason for the differences in color in my CP image as well, and I don't even remember if I have PMS Spot colors and am far too lazy this morning to double check yet. Drop the info on us on how to do that. I seem to remember a drop-down menu for it, but is there more to changing the color pallette than just checking it and saving?
30 degree angle cut on front and back of top piece to make it flush vertically.
Any chance of seeing a side profile shot of that? I think what you're saying won't be readily apparent to a lot of folks, as they normally look flush from straight on. The profile shot will demonstrate better what you are trying to convey. The plans show it perfectly, so if you don't have a shot of it, if there's someone who doesn't get what he's saying, just check the plans and look at the top panel of the cab. BTW, the re-worked plans look THUPER! What'd you use to create 'em?
Dunno how far you are yet, but those miscuts and the notching you have can easily be fixed. You said on your website you went to HD for parts, pick up a 2x2 "Handi-panel" of MDF. Should be large enough and cheap enough to just redo that piece if you want. I know it sucks, but just you mentioning it makes it sound like you're like me....you'll use it, but you ain't happy

Gotta buy some spray adhesive to attach the overlay
3M 75. Just enough tack to it that if you misalign it, you can still pull it off and realign it. The 77 version and other sprays seem to be more "extra strength" which is fine if you're just slapping it down and are an ace at it. The 75 version will hold that thing just fine after you've got it where you want it, with the benefits I mentioned. I used to work at a printing factory where we used the stuff to adhere postal labels, so I've got dozens of cans of it lying around. I haven't seen it in stores, so dunno, but check the uses and if they say it's repositionable. That 77 stuff sets up WAY too quick for my tastes....mebbe take a scrap of paper and MDF and "test 'er out" while you're there to see for yourself