Weight differences between Mater Cylinders.

Weight of Cast Iron 7/8" Manual Brake Master Cylinder
3 lbs 5 1/8 ounce

Weight of Aluminum Step Bore S-10 Master (24mm / 1 1/4" step bore)
2 lbs 8 1/4 ounce - difference of 12 7/8 ounces or a little over 3/4 lbs over the cast iron unit

Weight of an Aluminum Mopar / Strange style master cylinder
2 lbs 2 3/4 ounce - difference of 1 lb 2 3/8 ounces over the cast iron unit