I have used R/C mounts on several stunters.  When I started using the 46VF's in the mid-nineties I went to soft mounts and used the typical r/c mount with the soft mount bushings.  I shaved two ounces off the nose weight by thinner woods, etc because I felt with the reduced vibration I didn't need the strength that hard mounts required.  Did it help?  I dunno.  I flew the original Ephesian three years with no ill effects.  BUT- was I simply overbuilding before ?  Maybe.
I went to radial r/c mounts with NO soft mounting later with a couple of my PA's when I went up to the 61 & 65.  They worked fine and both ships done that way had many flights on them.  I think I saved one ounce nose weight in those.
However - (you knew there'd be a "However" didn't you?)  With judicious building throughout the whole ship I have used beam mounts for the last three serious ships while keeping the weoght very respectable and have suffered no problems at all.  Weight can be kept down with either method of building and I see no advantage of one over the other to be perfectly framk about it.
Blessings,
Will

Where the Hutch at (Don that is).  In his Stearman there is no motor mounts.  The plane he built and published had no motor mounts as such.  Seems he grinds of the mounting lugs of the engine.  Makes a back plate mount and uses longer screw for mounting to the back of the engine.  I would do it bit am afraid of messing up a good engine.  DOC Holliday

Hi Doc,

Bob Palmer's MARS has the three bolts for the Fox 35 back plate used as both engine mounts through the firewall and to hold the clips for the nose wheel!  I built ours with a R/C (Kraft Hayes??) mount and used "J" bolts to hold the nose gear.

Ted's Imitation uses a K/H type mount, and Aaron modified his Tutor (original TF kit) to this configuration after the third or fourth rebuild (he was learning! LOL!!).

Ken,
I have used the Sullivan slant tanks since '90 with great results as to ease of plumbing.  However, your possible solution sounds like a good one to me.  Be aware that I drilles my K/H mounts out for the soft mount bushings with no failure of the mount after years of flying those airplanes.  Your drilling a hole should not harm the integrity of the mount at all.
I think you would like the slant tanks though.
Blessings,
Will