Patent US4661815 describes the architecture and customization method for those chips. They're made of predefined i/o structures framing multiple columns of double CMOS transistor pairs called “Basic cells” (BC), spaced by empty columns for routing.

Customization is done by connecting the transistors with metal to form standard logic cells, which are then connected together and to the i/o structures.

Red: input to cell.
Green: output from cell.

All pictures are from 315-5674.

Input pin

Trace connects right behind the bonding pad.

Output pin

Trace connects to both N and P power transistors.

Bidirectional pin

One trace for input, and two individual traces for the N and P power transistors to allow tri-stating.

Output driver

Just a power inverter. Uses 3 BCs.

Bidirectional pin driver

Top input is output level, bottom input is enable. Outputs go to the pin structure transistors. Described page 10 of the MBCG25512 datasheet. Uses 5 BCs.

Inverter with 0.5 drive strength

Uses 0.5 BC.

Inverter with 1 drive strength

Uses 1 BC.

2NAND

Uses 1 BC.