Okay I went and tried to fix my problem with 'dead area and clunk sound' when changing directions today.
It turns out the old bolt shaft is 1.358in long (1 3/8ths?). Went to bunnings, but they only had up to 1" long of 1/4" UNF bolt. While I was there I decided that dealing with stripped nuts was a PITA and I'll just go with 1/4" UNC instead.
I could only get 316 grade stainless 1/4" x 1.5" UNC. Came home and went to undo the old bolt, and its ****ing stripped! Spent a good while jiggering around and finally got the bolt to bite on the shaft after slowly prying and tapping with a screwdriver and mallet.
Put in my new SS bolts and did her up and.... still ****ing clunking. Okay, did her up uber tight... snap! Grr.
Okay so I put a new pair in there (I'm using nylock a nut). Undid U-bolts, pushed the car around, did em up. STILL CLUNKING!?! (#)$*(#$
I decided it's either the rack or some crud around the tiebar ends. Jacked her up and doused the tie bar ends in WD-40. The rack boot on the driver's side has torn, so I cleaned and tied it back up with a cable tie. Not a perfect seal, but a bit better against grit.
Cleaned the ball joints with WD-40 and a rag also. It seems grease oozes out after greasing and attracts all this grit. Its worse than 100-grit sandpaper! Wiped all that up.
Went for a drive and....... NO CLUNKING!

There was nothing wrong with the pinch bolt or U-bolts all along! What a waste of time
Okay, so now I'm expecting you guys to tell me that going 316 stainless and UNC is bad and I'm gonna crash into the WTC and bring it down right?
hg.
Edit: 316 grade