Here's a brainstorm: How about modifying a game genie shell serve as a Mini Cart? Basically, switch the order of components around, with the main cart plugging into the mini-cart. This would also allow for use of the main cart without a mini cart, as the main cart can have all of the required components, with the mini cart simply overriding the appropriate address lines on the way to the NES. If this is possible (I'm not claiming to be an expert, just someone with theories) this solves both the need for a dedicated cart, and for a mini cart system, without having to develop 2 different prototypes. :)

Probably the best would be to have the battery-backed WRAM on the mini-cart, unless you need to replace graphics as well. In that case, the CHR-ROM would need to be on the mini-cart.

Pinouts on RAM chips, not really knowledgeable about such things. The net should have plenty of diagrams of RAM chip pinouts though.

As far as your earlier question about mapper, It depends on the program's needs. You probably won't know for sure until an initial design is laid down. For save games, you will at least need a mapper that supports WRAM. MMC1 and MMC3 seem to be the most standard mappers supporting 8K of WRAM. If the program is really advanced, MMC5 can be employed, but its trickier and rarer than MMC3. You won't know for sure what mapper to use until you know what your program's bankswitching and IRQ needs are.

Phoenix