I took a dove bar off a 1m Primestar, but didnt hook it up to see how it worked. The Oval Primestars ( 60e.75e, 84E) feedhorn has a line cast into it, and the LNB's, especially the aluminum cased ones, have a line stamped into them. You line them up, and you are at zero skew, if you install it on the dish vertically at the TS satellite. I think I still have the dovebar, if I do I'll check and see if I can discern the mounting position for ya.
I had good performance with the regular Invacom circualr/linear combo on an 84e and a 1m, but I agree with the crowd, no matter the LNB, you should use the stock feedhorn for optimal performance..