Do not take this personally, your customer can if he wishes, but...
$12K for a discontinued motor, adaptor and tranny customized by an overseas vendor is absurd.
The tranny may "better withstand" the 2.8 power but will it "fully"? Doubt it.
"slightly different direction"? Sounds like he came to his senses.
Now let's wait for someone as crazy as him to buy this stuff.