HI Wayne

I use  5 3\4  to 6 ounces with my  PA 51
I use  6ounces  with the 61
and  I use  6.5 ounces with the 65

Other  will use  the  same  or  a little  more

as far as the tank goes, typically a  1 inch tank will sit on the  same  plane  as the  motor,  or  be  shimmed  just  off of the beams  maybe  1\16 inch

If your  using  metal pads on top of the motor mounts  you will need  to add  at  least  that thickness  as  a  shim  under  the  tank

With thicker plastic tanks  you should be  OK  as  long  as  your  running  a  motor pads  under  the engine.  if  you  have  to move  the  thick tank  closer  to th e motor mounts  and  have  zero  room.  you can  just  move  the  uniflow  tube  upward  toward the mounts,  this  has  the same  effect as  moving  the  tank

Regards
Randy