I've paired this 1970 lens with my Lumix GH-2 for astonishing results. Its effectively 800 mm. Its razor sharp (the softness at the edge of the lens is gone because the MFT sensor only looks at the center of the lens. The bokeh is unbelievable even at f6.8 (because of the use of the extension tube in the design). It focuses fast! (I prefer manual focus anyway.) Its lightweight and can be hand held. And (this may surprise you) its easier to find birds in trees with this long lens because you can pre-soght along the long barrel (as if it were a rifle) before looking in the viewfinder.
Also, it come apart into two pieces and fits in my camera bag.

I have the Telyt 400mm f/5.6 but not the f/6.8 version.

I may see if I can adapt it for the E-PL1. I'd be interested in how well it would perform..