Personally, I think the seller if FOS.
Almost doubling the size of a 750? Sorry, ain't gonna happen.
The jugs from an 1100 are no where close to those of a 750.
The 600 to 750 conversion would be more believable,
but 750 to 1375? Yeah right.
Not to mention, even if it was possible, do you know how much
more stress that is on your existing lower end?
There's no way the the 750 clutch would handle a 1375cc engine.
Which rods did he use? I've never checked, but I'd be willing to bet
the rods are definitely not interchangeable, which means he'd then
have to put 1100 pistons on 750 rods, which again, I doubt will even fit.
I don't believe it for one minute.
Gasoline is for washing parts, Alcohol is for drinking... NITRO is for racing!