To me it sounds a bit on the high side, but not unreasonable. It takes a few days to correctly check and assemble, mock up, tear down, correct, clean, and re-assemble an engine. The question is what exactly are they checking, and correcting? How are they fitting the cam? How many times are they torque the studs and bolts? What will they correct for free, or charge extra for? What block prep are they doing? Are they installing the frost plugs and painting the block? What oiling system, how complicated a system (If they are installing it?) I think for the price they should degree the cam too?
I can see a long block costing more. It takes a bit of time to disasemble all the valves, check spring pressures, measure and correct spring install heights, mock up rocker gear, measure for pushrods, check and correct intake manifold fit, ect. I was thinking more like 16 hours at $50/hour = $800?