the chevy housing has the same bolt spacing, but is a slightly different shape, and may or may not fit the thermostat [correctly].
i fiddled some with a spacer used on a chevy dirt track car, and while it fit on a big block water pump housing, it was a shape that looked odd on there, [at least to me] and required the bottom of the spacer to be machined to accept the big block thermostat. the chevy thermostat will fall through the big block housing, as it's the small size similar to the later small block and magnum size thermostats.