The master cylinder in the box with part number 10-1737 is a master cylinder for a Chevrolet Monza. Looks to be misboxed, but I wouldn't be surprised if they are actually trying to sell this as a g-body master cylinder. This master cylinder will bolt up to a g-body firewall and function, but mounting it on a g-body firewall will put the master cylinder at an angle and will decrease to volume of fluid held in the reservoir and the level will need to be checked more often. It is not designed for an angled firewall.
I have had better luck with the $50 to $60 master cylinders than with the $20 to $30 master cylinder. The $20 to $30 master cylinders are hit or miss in quality. Its better to spend your money on a quality master cylinder than go through the hassles and issues with changing out a master cylinder more than once.
Regardless, all g-bodies with manual brakes or vacuum boosted power brakes should all have the angled plastic reservoir . From my experience, all g-bodies came with a master cylinder with a plastic reservoir. 1978-1981 had strait bore master cylinders with plastic reservoirs and 1982 - 1988 had step bore master cylinders with plastic reservoirs.
*All 1978 - 1981 manual brake master cylinders were cast iron with the angled, plastic reservoir. They had a 7/8" strait bore.
*All 1978 - 1979 power vacuum boosted master cylinders were cast iron with the angled, plastic reservoir. They had a 24mm strait bore.
*1980 - 1981 power vacuum boosted master cylinders were either cast iron OR cast aluminum with the angled, plastic reservoir. They all had a 24mm strait bore.
To my knowledge and understanding, no g-body was equipped with manual brakes after 1981 model year. All 1982 - 1988 master cylinders were aluminum and step bore with an angled, plastic reservoir. These had a primary bore of 1.25" and a secondary bore of 24mm. The step bore master cylinders were needed to operate, the new for 1982 model year, infamous LOW DRAG CALIPER. New, step bore master cylinders are cast iron. There are no new aluminum step bore master cylinders that I know of.
From my experience when installing:
*Rebuilt master cylinders = headaches. Buy new and more expensive master cylinders. Rebuilt ones are hit or miss in quality.
*Step bore master cylinders = headaches. Hard to bleed, more internal parts to fail, and secondary bore of 24mm is too large for stock sized calipers when running manual brakes.
*LOW DRAG calipers = headaches. These low drag calipers only work with step bore master cylinders and will need to be changed out if you want to run a strait bore master cylinder.