The intake and exhaust manifolds, and water pump are the same. The rest is different.
The L-48 was the base engine, It had approximately 190HP. The L-82 was the high performance engine having 220HP most of the years it was available. The last year for the L-82 was 1980.
L82 has a little more compression and even more cam lift & duration.
The L 82 is basically a leftover LT 1 design,has the steel crank,four bolt mains,does not have the compression ratio and valve train/cam as the LT 1 did,solids vs hydraulic lifters and has the larger 202 valves,stronger hydraulic cam then L 48 and an aluminum intake.
The L82 had about 35 more horsepower than the L48.
The L 48 is the base motor,cast crank,two bolt mains,lower compression ratio,hydraulic lifters as the L 82,milder cam then the L 82,smaller valve 194's and a cast iron intake L 48 has better low end pull then L 82
L-82 was a 4 bolt main whereas the L-48 was a 2 bolt.
The L48 replaced the L75 in 1969 as the base '300hp' Corvette engine. It continued in this capacity largely unchanged thru 1980. It was also an optional engine on a few other Chevrolets such as the Camaro.
The L82 came out in 1973 - essentially it replaced the L46 (last seen in 1969) as the '350hp' optional engine. It also was avail thru 1980.
The 300 and 350 hp terms are relative to the days before SAE Gross HP ratings. In '72 all HP ratings changed to SAE NET and subsequently dropped.
THe L82 had the old L46 cam. The L48 had a milder cam which produced great torque and a good idle.
L48 had a cast iron intake, L82 had lighter aluminum.
L82 and L48 have slightly different timing curves.
L82 and L48 have slightly different heads w/ the L82 having larger valves.