Thanks so much to upallnight, wpoll, and smokeyyank! After many long desperate months, the clunk noise is now resolved!

I actually got both problems that you mentioned:
1. One of the front bushing in the tension bar - driver side was completely shot. I replaced it. I also replaced the driver side since the bushings got serious cracks
2. Two bolts from the re-enforcement plate were loose, one from each side. They were the ones that also held the torsion bar - right above the plate. I think the majority of the clunking was from these two bolts

My car now drives so smooth, quiet, and solid, without any clunk!