Octopart links to chips in BOM

13    U1, U3   PAL20L8 or better e.g. 22V10
14    U11,U12  27256    
15    U14,U15  74ALS573 Transparent latch, 8-bit
16    U2       74LS74    
17    U4       74LS32   
18    U5       74LS646 Octal bus transceivers and register
19    U6       74ALS00   
20    U7       74LS175   
21    U8       NS32202 Interrupt Control Unit
22    U9       74LS30   
23    U10      74LS04   
24    U13      NS32081 Floating-Point Co-processor
25    U16      NS32201 Timing Control Unit
26    U17      NS32016 Processor
27    U18      DP84412 Replace with PAL16R6 or better e.g. 16V8
28    U19      NS32082 
29    U20      DP8419  DRAM address multiplexer and refresh row counter
30    U21      74S32   
31    U22      74LS08

The PAL chips are no problem, I have original PAL chips and the logic can be ported to modern GAL chips.

UT Source have the DP8419 and DP8409