Light wispy smoke out of right bank at highway speed

[ViviensTractor5110]

Ladies, gentlemen...

I'm grateful to be back in an audience with some of the most knowledgeable people around...fresh off a banning from our beloved board.

Anyways...I recently dumped the 250 and threw in a small block 400. Motor runs great aside from this scary fact...when I reach highway speed a very faint trail of smoke is left behind my right exhaust. I know it could be a million things, the curious part is that it only occurs at 2500+ rpms cruising...not necessarily under hard acceleration. Start up...low rpms..idle..acceleration are all clean. Any insight is very much appreciated.

The plan is to start yanking plugs tomorrow and going through the motions but I'm a little freaked and need to borrow a compression gauge as yet...wondering if anyone has seen similar...hopefully something stupid like a valve guide or clogged breather but I'm not lucky enough for that.

As a side note it runs ice cold...160 with no shroud...before all the steam hole Siamese cylinder talk starts.

Thanks again