Sorry for bringing this old topic back... but,
did somebody already see a stock
water pump housing that wasn't drilled for the bypass? I'm having some weird temperature spikes at idle when running a thermostat in my stock 383 HP. Without a thermostat everything is fine, besides running a bit too cold. After reading this thread I'm sure that the missing bypass is the reason for this, but I'm curios why the stock housing doesn't have a bypass at all. Every picture of a #2780987 housing I found has the bypass drilled.