I forgot to answer about the W and R compatibility...
... nope, not at all. Both front housings use 9 bolts, but the pattern on the R-series' housing is larger than the G- and W-series' pattern (which are the same).
So you would have to make a custom bellhousing in order to make your drivetrain weaker.
Also, in a similar sense, G- and W-series bellhousings do not fit on the front of a R-series transmission. This was one of the first things I looked into when I was doing my 3RZ conversion. I would love to have a R151F behind my 2.7 engine but its gonna require a custom bellhousing and its really not that important to me right now.
