1. Head bolts on OEM SBC blocks go through to the water jacket. They may be blind holes on performance blocks, but not on plain ol' ordinary blocks.
2. Yeah, the block drains are under-utilized during service procedures. As such, the bottom of the water jacket is likely filled with rusty debris. Not uncommon to have to poke a screwdriver or awl into the block drain hole to pierce the crust before the coolant will drain. When reinstalling the knock sensor, be sure to torque appropriately. The knock sensor, the drain plug, and the head bolts should all get their threads sealed with an appropriate thread sealer after cleaning the drain plug holes and head-bolt holes with a round wire brush to remove rust and dreck. Some guys run a dull tap or thread-cleaning tap through the threaded holes to clean 'em without removing "good" metal. I suggest Loctite/Permatex 592, NOT "blue Loctite" which is probably 242. When it's my own vehicle, I install a brass draincock instead of the stock iron/steel plug.
3. The TBI intake has a big water jacket on the underside. It would drain that coolant back to the heads through the ports nearest the thermostat, and then into the cylinder block; but the rear ports are mostly obstructed by the intake gaskets. As the water jacket on the intake is irregularly shaped, I'm sure it traps some coolant.
2. Yeah, the block drains are under-utilized during service procedures. As such, the bottom of the water jacket is likely filled with rusty debris. Not uncommon to have to poke a screwdriver or awl into the block drain hole to pierce the crust before the coolant will drain. When reinstalling the knock sensor, be sure to torque appropriately. The knock sensor, the drain plug, and the head bolts should all get their threads sealed with an appropriate thread sealer after cleaning the drain plug holes and head-bolt holes with a round wire brush to remove rust and dreck. Some guys run a dull tap or thread-cleaning tap through the threaded holes to clean 'em without removing "good" metal. I suggest Loctite/Permatex 592, NOT "blue Loctite" which is probably 242. When it's my own vehicle, I install a brass draincock instead of the stock iron/steel plug.
3. The TBI intake has a big water jacket on the underside. It would drain that coolant back to the heads through the ports nearest the thermostat, and then into the cylinder block; but the rear ports are mostly obstructed by the intake gaskets. As the water jacket on the intake is irregularly shaped, I'm sure it traps some coolant.
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