Features of Note:

• Rough casting in the lifter valley area.
• Holes in the lifter valley are broken out for oil drainage.
• The top of the rear bellhousing does not have the pad or hole for a knock sensor.
• The block casting number is on the top of the bellhousing area instead of on the driver's side as it is on later blocks.
• Casting for the water jackets and deck surface, for the head gasket, more closely follow the shape of the cylinders.

Features of Note:

• Hollows behind the water jackets of the rear cylinders.
• No pressed in freeze plugs in the rear cylinder walls.
• Face of the rear cam journal is flush with the oil galley plug holes.
• Rear cam bearing plug is very shallow.
• Large casting bump visible for the oil drain behind the rear cam bearing.
• Does not have the support webs on the top outsides of the rear main bearing.

Features of Note:

• Pad on driver's side (top right) says 231 instead of 3.8 as on later blocks.
• Support webs from main bearings to pan rail have a flat cross brace cast in.
• Oil pickup hole is smaller.
• There is barely visible, in the slot behind the rear main bearing, an oil drain from the back cam bearing.
• The inner crankcase area is much more open around the lower cylinders
• The main bolts have 13/16" heads.
• The exterior of the block is cast smooth down to the sides of the crankcase and not stepped as it is on later blocks, also notice the triangle shapes out from the lowere bellhousing.
• The small holes on each side of the front exterior of the block were drilled for water drains. Not the GM recommended location of between the frost plugs.

Features of Note:

• Front cover area is flat, not recessed.
• Water inlet holes are more square shaped.
• Openning to the lifter valley is broken out, not machined.
• Front outside of the lifter valley is mostly smooth with two raised flat areas on the sides forming a wide "V" shape.
• Look closely and you will see the oil feed hole is plugged. This motor was last run with an exterior oil pump.