I bought this assembled and ready to run board from Retrospy Technologies.
SMD technology, so small and of high quality.

Description from the Retrospy store:
The KIM-1 RAM/ROM board is a custom board than expands the memory of the KIM-1 single board computer.

Features

• Can provide 8k blocks of RAM or ROM between 0x2000 & 0xFFFF
• Fills in the KIM’s missing RAM between 0x0400 and 0x13FF
• 2 pages of DIP switch selectable ROM, upgradeable to 4 or 8 with a 39SF020 or 39SF040
• Includes a pre-programmed 39SF010 containing 2 pages of common KIM-1 configurations (Xkim for SD Card, Eduardo Casino’s Xkim with support for IEC/1541 drives)
• Backwards compatible with Corsham Technologies’ KIM-1 I/O Board
• Includes full color manual and 2×5 pin IDC cable.

Inspiration taken from a design by Bob Applegate of Corsham Technologies, LLC.

This board can be added to any KIM-1 system, but the easiest way to add it is with the Retrospy or Corsham I/O Board. This board comes with a ribbon cable that plugs right into the I/O Board with no mess. By default the DIP switches are set so your KIM will have 5K of RAM from $0000 to $13FF and from $2000 to $DFFF. The extended monitor is from $E000 to $FFFF.

For PAL-1 users with the PAL-1 Motherboard Expansion Kit
– the RAM RAM between 0x0400 and 0x13FF is already on the PAL-1 board, leave that open.
– The usual PAL-1 configuration has ROM at A000-B000, the PAL-1 ROMs are made for that location
– Without the KIM-1 I/O card, just put a Dupont male-female wire between Pin 10 of the “To KIM” connector to Decode Enable of a motherboard connector or K of a KIM-1 Connector expander.

I bought this kit from Retrospy Technologies and built it to enhance my PAL-1.
Worthwhile to add not only a motherboard but also get KIM-1 Expansion and Application connectors!
Easy to build, high quality PCB, lots of points to solder with the six PAl-1 Motherboards connectors.

Description from the Retrospy store:

With this motherboard, you can connect up to 6 expansion boards to your PAL-1 at the same time. The motherboard also provides the Application and Expansion connectors found on the original KIM-1, enabling the use of original KIM-1 expansion boards.
NOTE: To do anything worthwhile with the Application connector you will need the PAL-1 2nd RIOT Expansion Kit.

Not all signals are routed to the Application and Expansion connectors because the PAL-1 doesn’t provide them, so there is no guarantee every expansion board will work. However, Corsham Technologies’ and RetroSpy Technologies KIM-1 I/O and KIM-1 RAM/ROM boards have been tested and are compatible.

Available signals on the Application connector:
+5V
GND
PA0-7 (with installed PAL-1 2nd RIOT Expansion Kit)
PB0-7 (with installed PAL-1 2nd RIOT Expansion Kit)
DECODE ENAB

Missing are KB Row 0-3, KB Col A-G, TTY KYBD + RTRN, TTY PTR + RTNR, AUDIO Out (lo, hi), AUDIO IN, +12V, K0-K5, K7

Available signals on the Expansion connector:
+5V
GND
A0-A15
D0-D7
SYNC
RDY
IRQ
NMI
RST
SST OUT
PHI2
R/W
/R/W
/PHI2
RAM/R/W

Missing signals are: K6, SST, RO (pin 38 of the 6502), Phi1 (pin 3 of the 6502), PLL Test. On Reb B Phi1 is also available.

The signals /R/W, /Phi2 and RAM R/W are regenerated with two logic IC’s, the (reverse engineered) circuit is show below. The circuit could be a bit simpler, 3/4 of the 74LS00 would suffice.

Add KIM-1 RAM/ROM boards

Any KIM-1 RAM/ROM board can be connected to the Expansion connector. The Retrospy KIM-1 RAM/ROM is an excellent one.
For the PAL-1 only the Decode Enable line has to be added. For exammple with one wire Dupont male-female cable, from a motherboard connector. Any RAM in the region 0-1FFF is already available on the PAL-1 itself and should not be enabled on a RAM expansion. And therefore no need for signals K1-K4, the chip select lines for that region.

This version of the expansion kit has some minor points to improve (2.2 will be a next version the designer told me):
– add Phi1, not used often but is available on the PAL-1 connector
– enlarge the PCB edge pads with some mm’s, KIM-1 boards detach now to easy
– the two logic IC’s can easily be replaced with one 74LS00, only one NAND port and two inverters are required