Hi, Bernard.
I can see dozens, if not hundreds of regulars on this group wringing
their hands over the possibilities of you and your friends ending up in
wheel chairs or worse over this one. Many of us are having visions of
our first such attempt watching as some little unforseen thing goes
wrong; at least spoiling the day, likley damaging the thing we got the
"deal" on, or, worse than that causing permanent personal injury.

I like "backlash"es recommendations.

Please do not try to move this stuff in mud even with plywood. The
wheels on your "forklift" (is it a pallet truck) are 'way too small.
The plywood will be pushed by the wheels wherever there is a joint
and so the load will drop down below the level of the next sheet. Think
about the poor mechanical advantage of trying to get that wheel back up
onto the plywood. I know that you wouldn't use any foul language at
this point, but I know that I have been sorely tempted.

Here's a slightly different take:
Look up "riggers" in the phone book. Try to work out a deal where
they do the heavy work on your end in trade for a sculpture that you do
for them. Everybody wins. They get something of value; you get more
practice at your art.

Also, I think I saw a disconnect between trailer capacity and stone
size. Get more trailer than you need, not less. Most general dyi
rental companies have 2 axle trailers for rent. They generally can hold
about 5000 pounds net. That way you could bring even more stuff home.
Make sure the trailer has (at least surge) brakes and DO spend the
extra rental money for tie downs. It your buddy doesn't have experience
driving the truck with a heavily loaded trailer behind, implore him or
her to drive carefully and drive way, way out in front! It's easy to
be going along having a good conversation, and having to do a panic stop
from inattention to the road. Without the loaded trailer, no problem,
but------.

Once a load that heavy gets out of control, there's no going back.
Don't ask me how I know this.

Think about medical costs and liabilities. After all, we do live in
litigious America. A healthy friend, even slightly damaged, becomes a
courtroom nightmare when his parents are presented with the medical bill.

Pete Stanaitis
--------------