It does mount to a flat surface. May be the photo's a bit misleading.
It's just that gap underneath that worries me.
That machined out, horse shoe shape mates up with the TPS.
Tried a gasket as you suggested, to try and block off that gap under the TPS.
No go I'm afraid.
It spaces the TPS out too far and the shaft can't connect to the TPS properly.
Mind you' I did use cork (that I had lying around) which I thought would be too thick.
Might try paper gasket material, as it's much thinner.
Although I don't think it'll work.
Here are some pictures.
I don't have a Factory T/B to compare it with unfortunately.
The first picture has the measurements of the connection to the TPS.
Yeah, that shaft doesn't look like it need the plastic sleeve as it seems a lot bigger than the standard TB shaft. I'll measure up a standard shaft later.