This is not true. Cylinder heads are the same. The only difference between the two, mechanically, are the intake camshafts (higher lift on the L37) and with the earlier engines, stiffer valve springs for the L37. Apparently, starting in mid 1996, all engines began to use the stiffer valve springs.
There is no change in displacement. Engines are exactly the same except for what's mentioned above. Any discrepancy is a typographical error in what you read.
Displacement is a function of crankshaft stroke and cylinder bore. The COMPRESSION RATIO is slightly different between a 1999 Northstar and a 2000 Northstar because in 2000, the heads were redesigned to recommend 87 octane fuel. I think the compression ratio went from 10.3 in 1999 (for both the L37 and LD8) to 10.0 in 2000 (again, for both the L37 and LD8). Changes made for 2000 are across the board and again, the only difference between the two engines is the intake cam profile.