Considering a Slant 6 swap into a Mitsubishi Starion...

No way I'd ever put the heavy boat anchor slant in a StarQuest!!! Those cars have lots of potential, and a S6 would be a step in the wrong direction!

And I love the ChryCo 2.2/2.5 and am currently building a S60 GLH, but there are engines with way more potential that go in the StarQuest with less work!

GM LS or a Mitsu 4G63 are the best two options imho...