1964 plymouth valiant Slant six to 340

Hello guys. I purchased my first car and im finally building it how i truly wanted to when I was 16. I have a 1968 340 that will be built up to 450 hp. I have everything settled except for the drive shaft. Any suggestions ? Im sure I cant use the orignal one or can I ?
PS i will be using a 8 3/4 with 3:91 gears

Sorry guys forgot to mention that I have a 64 A833 that im rebuilding which will go into this car. I have been contemplating going with the QA1 drive shaft since it will be having a QA1 front and back suspension already.

Any thoughts ?

Btw Im in Torrance, California

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