Peter,

I would say that the engine builder isn't liable until a tear down of
the engine reveals a failure point he is warranty.

The swap guy is only on the hook if: he billed you for the rebuilders
work on his invoice; or  performed work on the rebuilt motor, i.e.
torque heads; or some other such installation service to the rebuilt
engine. The it's the swap guy's responsibility to warranty anything he
billed you for if proven defective.

My suggestion is that the rebuilder suggest another shop to remove the
engine. And you could ask that the rebuilder split this cost if his work
is defective.

It's my opinion of fair.  I have rebuilt engines and repaired engines
others rebuilt but proved faulty, the conditions above were in effect at
our shop.

Sincerely,

Mark Keller
91 Carat