Where do I route the LS steam vent line on a square body swap?

Same answer as any LS swap — send it to either:

• a steam port on an LS swap radiator (most LS conversion radiators have one), or
• the upper radiator hose, through an adapter with a steam barb. Speedway's LS swap radiator hose adapter (listed at $24.99 in its article) fixes both problems at once: a 1/4 in hose barb takes the steam line, and it adapts the LS water pump's 1-1/4 in upper outlet to the 1-1/2 in inlet on a typical radiator. This works with the square body's original-style radiator.

On most LS engines the thermostat sits low, on the water pump, instead of up top like older small- and big-blocks. GM added steam lines in the cylinder heads to vent trapped air and keep hot spots from forming at the top of the engine. See how to route the steam line with no steam port.