The Darkroom Cookbook does not give any development factors for FP4+ at ISO 164, but the following alternatives are provided:

Xtol (no dilution): ISO 125--8 minutes
ISO 250--9 minutes
Xtol 1:1 ISO 125--10 minutes
ISO 250--12 minutes
Xtol 1:2 ISO 125--11.5 minutes
ISO 250--13.75 minutes
Xtol 1:3 ISO 125--14.75 minutes
ISO 250--17 minutes

You might still shoot it at ISO 160 and, based on the dilution choices above, select a time factor identical to or between the two given for each ISO/dilution factor. For example, since 160 is close to 125, with no dilution you might choose 8 minutes, with 1:1 dilution you might choose 10 or 11 minutes, with 1:2 dilution you might choose 11-12 minutes, and with 1:3 dilution you might choose 15-16 minutes.I have made this type of analysis and comparison before with other b&w films and developers and not experienced any problems or discrepancies.