GB cart with Ram, Rom, no MBC. How do they work?
The cart connector has a pin (which seems to be variously reffered to as "MREQ" or CS_SRAM) which distinguishes between access to the cart rom space and access to the cart ram space. I'm seeing conflicting information on line about the active polirity of this line so it may be nessacery to do some testing.

If you can find a rom and ram chip with the right chip select polarities you may just be able to hook them up directly. If the chip select polarities on your chips are wrong you may need an inverter. Definately no need for anything as complex as a memory bank controller just to have both rom and ram.