I used some S10 swap headers by Racing Innovation Supply. Not bad for $175 shipped.
http://www.ebay.com/itm/1982-04-Chev...72.m2749.l2649
As for motor mounts I made them. The ones mounted to the frame are common SBC mounts, think I got them from Rockauto. I had originally planned on a 283 so I had bought some S10 swap mounts, but the holes are different on the LS engine. I used them as a template, bought some 3/8 plate steel from my local salvage yard and went to town.
I will mention I have the engine lower than other builds I have seen, I really wanted to reduce or eliminate the hump on the floorboard. I also have the cab mounted pretty low so I had some room to adjust there, too. I do have an issue with my oil pan sitting too low (~3-4" below front cross member) but I plan on changing pans and making a skid plate. I also had to take into consideration the inclination angle and I have it to about 3-5 degrees, should be more to the 3 degrees when I get radiator, coolant, front clip, etc. mounted.