This sort of vague term has always done more harm than good....
A source should specifiy *which* density, rather than calling it "half" or "low" or indeed "high" or "double" or whatever - as what was "high" density in 1998 (when the i440BX came out) was "low" or "half" density by 2000 (when the CUBX was released) 😮
i440BX can support max 128Mb chips. That is the only correct statement about density. A regular unbuffered SDRAM DIMM can hold max 16 of those chips in a dual rank configuration. 16x128Mb=256MB.
So, you need 256MB DIMMs with 16 chips, and the chips need to be of the 16Mx8 (not 32Mx4, frequently marketed as 'Via only', not JEDEC compliant and usualy only from shady vendors). Find four identical 256MB DIMMs with 16 chips each from a reputable brand (Micron, Infineon, Nanya, Samsung, TwinMOS, Hynix etc) and you should be good to go.