[glennpm]

Regarding the gasket coolant holes, they were Ford design changes to address overheating complaints on the earlier blocks. The larger block holes may have improved removal of sand whereas the smaller gasket holes, controlled coolant distribution in the block. Below are a couple of pertinent AI search results.

"The small top water holes in 59A Flathead head gaskets are intentionally designed to restrict flow and force coolant to travel to the rear of the engine rather than taking the path of least resistance straight out of the front cylinders. If these holes were enlarged or if large holes were used, the coolant would bypass the rear cylinders, causing them to overheat due to insufficient cooling.

Flow Distribution: The gasket acts as a metering device, using smaller holes at the front to encourage water to circulate further back where it is needed most.
Prevention of Shortcuts: Larger holes at the front would create a "shortcut," allowing coolant to return to the radiator too quickly without absorbing enough heat from the entire engine block.
Manufacturing Necessity: Engine blocks are sand-cast with larger holes to allow sand to be removed during casting; the gasket's smaller holes correct this to ensure proper flow patterns.
Using the correct small-hole gasket (such as the FP7283B or equivalent) is critical for the 59A engine, as modifying the holes or using a gasket with larger holes can lead to gasket failure and severe overheating"

"The 59A-B head gasket for Ford Flathead engines uses round holes in the center because this configuration was the design point for controlling water flow distribution, specifically to send more coolant to the back of the engine for better cooling efficiency.

According to Ford technical guidance and forum consensus, the gasket holes are intentionally sized and shaped to restrict flow rather than match the larger casting holes in the block, which are primarily for removing sand during manufacturing. Using the all-round hole version (as opposed to the earlier trapezoidal holes used on 1938-42 heads) ensures that coolant travels the full length of the block before entering the heads, preventing "shortcutting" where water would rise immediately at the front and leave rear cylinders overheated.

Flow Direction: The restricted round holes force water to flow rearward through the block, up into the heads, and forward to the thermostat.
Manufacturing vs. Design: Large holes in the engine block and heads are often casting sand removal holes that are bigger than necessary for cooling; the gasket holes are smaller to meter the flow correctly.
Recommendation: Experts advise not drilling or enlarging these holes, as doing so would bypass the cooling path for the rear cylinders and cause localized overheating. "

Bottom line, use the later 59A gasket for your bored 221CI earlier block.