4,500 dollars for a 8 & 3/4 .....?

I searched: magnesium mopar rear end

What did you search google with, MAPS ????

How to Build the Right Period-Correct Pontiac/Olds Rearend for your Gasser

This result popped up just after the searched showed the Kiiji ad for the Mag rear you are talking about

Technical - Mickey Thompson rear carrier

Mickey Thompson magnesium Mopar 8.75 3rd member posi | Transmission & Drivetrain | Winnipeg | Kijiji

Here's that rear end for sale that was also listed here on FABO. He probably more than this in parts and labor purchases. But it's used race parts and he's not quite factoring that in. And you can see why a new strange Dana starts looking like a viable alternative to throwing big $$ at a 8.75.

Mopar Aluminum Strange A Body Racing 8 3/4 Rearend for sale in ESCONDIDO, CA, Price: $2500