'70 Mustang Convertible Sheet Metal Question

So I have finally bitten the bullet and the convertible is nearly completely torn apart. I have found that the rear quarter panels are actually a lot better than I thought. I believed that they were full of mud.

The problem is that the outer wheel houses on both sides are rotten. It is really odd in my opinion that the wheel houses are so bad and the quarters are so solid. I pulled a bunch of fiberglass and bondo out of the area between the two. Maybe someone replaced the rear quarters in the past but left the wheel houses alone? I'm not sure how to explain this.

Anyway, my questions: does it make any sense to cut out a good quarter panel skin in order to replace a bad wheel house? If I decide to cut out the rear quarters, where should I cut them? I'd rather not buy the super expensive full convertible quarters from Dynacorn, but I might do that if the other options are much worse. I know there are some real experts in sheet metal replacement on this forum and I really hope to get advice.

I've been thinking the quarters should come off so that it's easier to clean and paint the bracing behind them. The bottoms of both wheel houses and the rear torque boxes are very rotten, but higher up inside the car everything has surface rust only. The tops of the convertible wheel houses are flattened, so I will have to replace only the bottom sections of them.

I was hoping you would reply, Jim. I guess my next step is to sand the paint off the quarters to be very sure that they are actually in good shape before I spend the time to drill all the spot welds.

Thanks for the additional information!

I sanded the paint off both rear quarters. The driver's side had some significant dents and holes in it under a heavy layer of filler, so I've started cutting out the driver's side. I'm still hoping to save the passenger side. It is in good shape as far as I can tell.