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Other then checking the numbers, there are two basic visual differences. The L82 used finned alumn valve covers, L48 uses stamped steel (but this is an easy swap and as such not an accurate test). Second is the best, the L82 uses 8" harmonic balancer while the L48 uses a 6 3/4" one.
But the only real way to tell is to check the stamp pad numbers.
By the way, the 5th digit of the VIN will tell you what it was as it came from the factory, 8=L48 and 4=L82. The stamp pad suffix of ZBA or ZBB would be a 79 L82.
Watch the valve covers, though. You could buy them aftermarket; I have them on my L48. I have a '78 L48, so I know many of the differences. First off the comment about the engine stamping is the best. The car serial number will also reflect the shipped engine. Other indicators:
Finned valve covers
All '78 L-82s had A.I.R pumps. If it's removed look for the "traces" of it
Dual snorkel air cleaner
engine serial number
Car serial number
Larger exhaust 2.5" vs. 2.25"
Watch the valve covers, though. You could buy them aftermarket; I have them on my L48. I have a '78 L48, so I know many of the differences. First off the comment about the engine stamping is the best. The car serial number will also reflect the shipped engine. Other indicators:
Finned valve covers
All '78 L-82s had A.I.R pumps. If it's removed look for the "traces" of it
Dual snorkel air cleaner
engine serial number
Car serial number
Larger exhaust 2.5" vs. 2.25"
Those are good indicators for a 78, but on a 79 L-48's had that equipment as well. The Only for sure way is the numbers on the engine - and even those can be faked, however that is very very unlikely. The VIN will only tell you what was shipped with the car and not what is under the hood at the present time.
Watch the valve covers, though. You could buy them aftermarket; I have them on my L48. I have a '78 L48, so I know many of the differences. First off the comment about the engine stamping is the best. The car serial number will also reflect the shipped engine. Other indicators:
Finned valve covers
All '78 L-82s had A.I.R pumps. If it's removed look for the "traces" of it
Dual snorkel air cleaner
engine serial number
Car serial number
Larger exhaust 2.5" vs. 2.25"
Those are good indicators for a 78, but on a 79 L-48's had that equipment as well. The Only for sure way is the numbers on the engine - and even those can be faked, however that is very very unlikely. The VIN will only tell you what was shipped with the car and not what is under the hood at the present time.
Checked the numbers (matching, VIN and block), my 79 is a L-48.
It had stamped steel valve covers, 2.5" exhaust and had plumming for a Dual snorkel air cleaner but only had a singal snorkel air cleaner on it. Thats what raised the question. I've bought a Dual snorkel air cleaner to put on it.