Funny...

MACO only mentions 12(yellow), 22(orange), 25(red), 29(dark red), 70(very dark red), 88A, 87, and 87C (Black, IR transmitting) on their website...

No mention of 89C on mahn.net, nor in my "filter bible": CRC Handbook of Chemistry and Physics, 62nd edition. There is an 89B, with 50% transmittance at 720nm, however...

The 50% point are (roughly):

25: 600nm
29: 620nm
70: 680nm - narrow band filter
87: 795nm
87C: 860nm
88A: 750mn
89B: 720nm

So 87 and 87C would be very dark for MACO 820, almost totally black for Konica IR750. 89B looks more promising, and is equivalent to what is sold as "R72". 70 would give about the same results as 89B with IR films - except Kodak HIE, where it would cut off some of the far infrared.