xx4256 = 256K x4 (8 pcs for 1MB bank), page mode
xx4258 = same with static column
Mixing SC and PM ZIPs works but then the first bank must not be SC throughout.
Since the 256K x4 chips limit your fastram to 4 MB max, I'd look for a SIMM adapter. 32 pcs of 1M x4 ZIPs would be 100€-200€+...
PS: You can also use standard DIP chips xx4400 for the first bank instead of ZIPs, just leave the first bank ZIP sockets empty.