Using this info I got it to work now:
systInfo:
+0x80 = ORDER ECONOMY (typeID)
+0x84 = invested industry
+0x88 = ID of building/ship under construction
I'll summarise all needed code changes, including those by DCER (redundant data was omitted ->single buildings/ships).
At all locations change 0x66 to 0x90 (unless otherwise instructed):
=>
Buy Cost calculation fix:
43E000 mov ax, [ebx+4] -> 0x
3D400
43E03A mov ax, [ebx+4] -> 0x
3D43A
=>
Buy cost preview fix:
45F6E9 mov ax, di -> 0x
5EAE9
=>
Effective build/buy cost fix:
46055B mov ax, [esi+4] -> 0x
5F95B
460566 jbe loc_46089B -> 0x
5F966 change
0F 86 to
90 E9
4606C8 mov dx, ax -> 0x
5FAC8
4606EB mov [esi+4], dx -> 0x
5FAEB
4606F1 mov dx, [esi+4] -> 0x
5FAF1
460703 add [edx+2Ah], ax -> 0x
5FB03
4608A2 mov ax, [edx+2Ch] -> 0x
5FCA2
4608A6 add [esi+4], ax -> 0x
5FCA6
=>
Sumary / Systems -> "X Turn(s)" fix:
44195F mov ax, [ecx+4] -> 0x
40D5F
441A4D mov ax, [ecx+4] -> 0x
40E4D
=>
Production Queue -> "Turns Remaining X" fix:
4F2E57 mov ax, [esp+22Ch] -> 0x
F2257
=>
"Industry Invested" display fix:
4FD998 mov dx, [edi+84h] -> 0x
FCD98
4FD99F test dx, dx -> 0x
FCD9F
4FD9B3 mov ax, dx -> 0x
FCDB3
=>
high morale bonuses fix:
0043FA55 mov dx, [ecx+4] // 0x
3EE55
0043FA62 mov [ecx+4], dx // 0x
3EE62
=>
Ship stats build cost above 32767 fix:
0x
17EBE2 -> change 0x64 to 0x75
I don't know how many bugs is too many but that point is reached somewhere before however many in BotF is.