Whut, you ain't got no GM door/trunk decals? It's easy peasy, hoss.
If you ain't got them, lemme dig around a little. Got that info around here somewhere when I restriped mine. But I had GM decals which made it a WHOLE lot easier for the doors, although the trunk application you wouldn't want to use the GM guideline as it will kick the inside of the decal higher than it needs to be and look kinda strange. Ask me how I know.
After all the fenders and doors and what not are aligned properly, THEN do the decals. Otherwise if you adjust doors and fenders after the fact, it'll mess up the alignment. I'd start with the quarterpanels and front fender skinny upper and lower wide stripes first. Then, after they're done, THEN the door upper and lower stripes can be applied to allow them to line up properly with the other stripes.
The lower side decals need to be placed on the car over the wheel wells which can happen at any time, as long as it's before the door
Hurst/Olds decals are placed. And THEN you can put the door stripes on so you can align them to match the ends of the stripes where they meet at the door.
Of course, if that's already done, then you just need to measure. Like I said, give me a bit of time to drag that up.