Somethings wrong here.
There's nowhere on a real railroad that you're going to find a "block" 50 "scale feet" long. An engine won't even fit into that.
Typically, blocks could be anywhere from a mile (or perhaps less) long, to 3-4 miles in length, sometimes longer. HOW long would depend on traffic type and traffic density. The blocks inside the tunnels to Grand Central were about 1/5 mile long "back in the day", and you could follow trains quite closely there, but the speed limit was 35mph, and only passenger equipment (with better brakes than freight) was permitted.
For a freight railroad, or higher-speed passenger railroad, blocks would be far longer.
For a model railroad, blocks (between interlockings) would probably work best at 2-3x the typical train length (unless you run VERY long trains).
The best placement for signals would be at interlockings (switches and junctions), so that they "protect" the switches from conflicting movements.
Signals should be located TO THE RIGHT of the track, viewing them from the perspective of an oncoming train. There were exceptions in the real world, but this is the normal way of doing it in North America.