Need an 8 3/4 for my 69 Dart 413/727, help?

December last year I took my Dart back from a shop after the bill went crazy. It would only run hot wired. Fast forward for now and I need to replace my 7 1/4 with an 8 3/4. I saw some online for 4K+(if only I had more money). Motor is stock, 350hp assumed but would like to have 500hp or so later. Buy one and have it rebuilt? Costs? Is remanufactured worth it? Just for street but plan to put my foot in it a lot. 3.55 or 323? Thanks in advance.View attachment 1715882642
Start a wanted thread here on FABO. Complete 8 3/4 rears come up for sale from time to time. They go for good money but $1000-1500 is the going rate.