Re - EPROM pinouts; Games use 8-bit EPROMs.
So 4Mb is 512k x 8. Any EPROM (UV eraseable, OTP, EEPROM) with this data format will work, as the pinouts are standardized. (Flash based EPROMs, not so much.) The most common are 27C040 and 27C4001 for 4Mb, 27C020 or 27C2001 for 2Mb. (Yeah, there's a pattern here!)

Figuring out which chip to use is not difficult either - take the size of the file on your hard-drive, multiply by 8. (So, a 4Mb ROM will accept a 512kb file. 2Mb will be 256k.) To find the size of the file, take the EPROM size, divide by 8. (It's that whole 8-bits thing, see. )

Yup, what they said.
Because of how chips are addressed, and the circuits are designed, the game could get garbage back. Or the checksum not match right.
Also, pinouts BETWEEN the different versions are usually NOT the same. I.e. A 27C020 does NOT match a 27C040. May be *close*, but not exact. (Usually because of the added address lines, needed to access higher chip memory!)

If you use a bigger chip, and the board can support it (WPC can..), then you must double the image. (Run the command copy /b file1 + file1 outfile)