I'm having trouble finding somehwere a20 and a21 on this board.  the eeprom slots have 32 pins not 36 and it looks like pin 46 on this board is unused.  I tried wiring the 74hct139 to pins 12 and 13 on the mad 1 one chip as I had read that those are an alternative, but still cant get my repro to load up.  I'm wondering if anyone has any knowledge of this board.  Here's a link for reference.

https://snescentral.com/pcbboards...

First of all, what kind of EPROMs/Flash are you using?
Secondly, cart connector #46 is A21 and you'd have to solder directly onto it.

MAD-1 Pin 1 goes to EPROM #2 /OE
MAD-1 Pin 16 goes to EPROM #1 /OE

If only using 1 EPROM connect /OE to MAD-1 Pin 4

Obviously (not tested) the MAD-1 only decodes A20/A22 leaving A21 disconnected since A19 being the highest address line here for EPROMs.

Since your EPROM/FLash has A21, you'd have to rewire MAD-1 Pin 12 and 13 probably.