I would be facinated to see this specimen.
My impression is that it's actually a .356wcf. M94 "BigBore", and not a converted rifle. At that price it would be a STEAL !!!!!
The bigbores in .356 are going for $500 and up.
A Marlin M336 in .356 are going for $1,000 and up.
OR........... Is it a Marlin M336 in .35Rem converted to .356wcf. That is a "doable" conversion, ballistics come "close" to .35whelen performance. Only caveat is that I've heard of some "feeding" problems with some of the conversions. I have thought about "converting" a M336 in .35Rem to the .358 chamber, but only use "handloads" of .356 level loads w/ round/flat nose bullets.
I don't see how you could chamber, feed, or extract an '06 length round from the M94 action.
I think you need to look a little closer at the action, barrel stampings, and see if you can get a .30/06 cart. to chamber if you don't have access to a .35 Whelen. And most importantly, extract and eject!
Having a .338/06 chambered rifle, and it being capable of better ballistics all the way around than the .35Whelen, I seriously doubt that the .35 is any more efficient.
The .338/06 uses the same powder charges (within normal variances between individual barrels/chambers) with identical bullet weights to get ~100fps higer velocities, and energies out to ground impact distance favor the slimmer .338 bullet all the way.
No "slam" against the .35whelen, I'm still considering rebarreling another M98 action to build one.
However, every time I use it, I decide the .35Remington is actually adequate to any purpose I have for a .35 and it is VERY Efficient. Especially at putting game on the ground.