Classic Media's release of Mothra vs. Godzilla uses the R2 DVD for the Japanese cut, and while it's OAR, it's pretty murky, soft and IIRC, sourced from a '90s era digital LD master. As for info on Godzilla vs. The Thing, see this post I made on Toho Kingdom: http://www.tohokingdom.com/forum/viewtopic.php?f=6&t=15751&p=648795&hilit=#p648795
...that's a whole 'nother can of worms I don't wanna open here.
Bottom line, if you just want the Japanese and English versions in a convenient form, it's pretty serviceable.