These JEGS 25000 bearing spacers will allow you to install a small block chevy 350 crankshaft with 2.450 in. main journals into a small block chevy 400 block with 2.650 in. main journals. No modifications required to the crank or block, just snap them. These spacers accept standard 350 bearings and must be purchased separetly for your crankshaft specifications. This spacer set is a great start for creating a 377 cu.in stroker.