in theory, the floor mounts seem like it should work fine. The osr2+ & sr6 should be able to mount on just fine.
Weight and drag are what you need to keep in mind with the OSR2+. The less weight
you ask the servos to move, the better they will perform. They’ll be quicker, more
forceful, smoother, and last longer. Additionally, you may not want to use your
tightest sleeve, as increased drag will have the same detrimental effects as
increased weight.
The heaviest ona I used on it was about 900g and that was only with the legendarylootz slow script. My other ona’s that I use frequently weigh 330g/370g/400g with scripts ranging from slow to speed demon and my servos haven’t had any issues so far since getting my osr2+ on March 20 of this year.
Hope this info helps.