I haven't had 1st hand experience with 66 and earlier Abodies with the milodon road race pan.

When it comes to a custom k-member fitment is going to be on the fabricator that's building the car.

What brand aftermarket K-member are you running? Maybe ask around if someone is running that same combo.

The kick up in the center is so you get a tall back wall to the sump to trap/keep oil in the pan. It makes the oil think it's an inch deeper pan. The low pro Milodon pans they've sold for years has the same kick up.

That small rear sump does not all fill with oil. It's mostly filled with the oil pump. Remember how you have to worry about HV taller oil pumps rubbing a stock pan? I it's cause the oil pump is so close.

The height of the rear section of a small block pan is only to clear the oil pump. If you ran an external oil pump the whole rear section could be shortened all the way back the same height as the kick up.