From memory (it's been years!) you want the "operating angles" in the 1* to 2* range, as near equal as possible. ZERO is not a proper target, as U joint needle bearings must "roll" or they will be beaten flat on one surface and fail.
YEARS ago (a decade maybe) I think old BNE himself was prototyping a T5 extension plate to enable proper fitment into the 7/9 shifter location. I think he built a few, as perhaps JohnV might have himself. If memory serves, Nathan also built/bought one. He's long been gone from OVLOV land, but BNE might still have a CAD file. The final solution is so expensive it isn't practical..... get the T5 Aussie trans tail section which places the shifter in the proper position.
If you search, you will find threads from about 5-7 years ago that beat this T5 length & shifter position topic to death......
Lastly - are there any T5 RWD users running a one piece driveshaft? I think YOSHI was pushing this years ago with his adapter kit. As those experienced in this swap have learned..... the T5 must be (1) properly rebuilt and (2) properly shimmed to reduce the strange 3K vibes (the title of this thread, I think). My opinion will remain, that if one were to use the FORD 4 cylinder output yoke (large dampener design), you will achieve the best T5 solution. Those FORD OE Engineers figured this problem out for those Turbo T-bird 4 bangers, all those years ago....... and their solution still works.