GM274M is a standard which covers a range of grades, firstly general purpose grades where Minimum Tensile can range from 125MPa to 250MPa. Followed by special purpose grades for Disc Rotors, Pump Bodies, Bearing Caps, Piston Rings and Cylinder Liners.
For the general pupose grades, the equivalent standards are:
G125 ASTM A159 G1800 or SAE J431
G150 ISO 185 150
G200 ISO 185 200
G205 ASTM A159 G3000 or SAE J431
G240 ASTM A159 G3500 or SAE J431
G250 ISO 185 250
Hope this helps
James