Hey Elliot, with design you will have to watch the loading, in a shop environment it would be better to over build (who knows what the loading will be over time.) In any case, 6 x 6 beams will likely not be able to carry the load. I would look at the capacity of 6 x 10's as a better option. On the scarf detail, I would extend the under scarfed beam so it safely captures the brace end. The scarf detail as drawn will have a separating reaction force imparted by the brace to the over scarfed beam. I'll vote for the joist over shooting the beam.