A bypass hose is a good thing to have on an inline 6. Because of the location of the water pump, #1 cylinder tends to run too cool and #6 tends to run too hot. Allowing circulation through the block even when the thermostat is closed helps to alleviate this, and keeps #1 from wearing out as fast.
Also, with a 261 a bypass hose is necessary to prevent steam pockets under cold start loads, due to the siamesed cylinders.
Chevrolet put bypass thermostats on for a reason, they would not have gone through the expense if they had not deemed them necessary.
I've also heard the the 292 pump has a baffle on it that the 250 pump does not, to help with the #1 cylinder cooling issue.
