Converting Spectra HLN6142A or HLN6143A to v6.16 Firmware??

[hvfcadmin]

Has any one tried converting a older 2.xx rev MLM Board to the latest v6.16 Firmware. I have two older MLM Boards, HLN6142A and HLN6143A, They currently have (1) AT28C64 EEPROM,(1) 16K SRAM Chip, (2) 27C256 Proms. I have converted the newer HLN6160 MLM's to the v6.16 but am having a little trouble on the older boards. I allready have the
BIN images from my other good v6.16 MLM.

After looking at the boards:

Both will support 27C512 Chips
Both will support 64K SRAM
Would need to move 3 jumpers to support memory changes

Problem:

1. Newer MLM's use Address 17 to select PROM2 Chip Select, Older MLM used Address 15
2. Newer MLM's have Address 16 going to PROM2 A15 and Address 15 going to PROM1 A15
older mlm's have both A15 lines off of PROM's tied togeather.
3. Newer MLM's use 74HC153 to handle Chip Select Functions, older uses 74HC00 4x NAND Gates.
4. when both A15 and A17 on newer mlm is logic high, then PROM2_CS is selected
5. when either A15 or A17 on newer mlm is logic high then PROM1_CS is selected
Older MLM selected PROM2_CS when A15 was logic low.

Just looking to see if anyone has done firmware upgrades to the older MLM Boards with out doing
heavy modifications.

So far the only way i can see to do it would be to remove the 74HC00 and deadbug a 74HC153,
then wire it up to match the HLN6061 revisions.

Thanks