How come a cam with a 509 lift is considered a HUGE lift on lets say a 327 smc?

How come a 560 lift on a LT1 is considered a decent lift?

 

Lift is only one specification of a cam. Duration, LSA, overlap all play a part in how a camshaft behaves.

The old engines were all flat tappet cams. 0.509 lift was a lot of lift for a flat tappet cam lobe plus the small factory valve springs didn't like much above 0.480 lift.

Modern engines utilize roller cams which can allow much greater lifts. Since the manufacturers already know a roller cam can give more lift than a flat tappet, valve springs are designed for the higher lift.

There's nothing from preventing you from upgrading an old 327 to a roller cam with better heads to use the higher lifts. The size of the cam also works differently in different engine. A .500 lift cam in an old 283 was a lot of cam while the same cam in a 400 would be tame.