Initially the producers approached the Japan Ground Self-Defense Force (JGSDF) for props and vehicles, but the army withdrew its support after reading that soldiers go AWOL in the script. For that reason, old and sometimes outdated equipment (like M3 sub-machine guns) had to be used. The tank featured in the movie was even built entirely from scratch.
The run time for this movie is wrong it's not an hour and 25 minutes it's actually 139 minutes well over 2 hours and this is a source from the GI Samurai the Sonny Chiba collection dvd.
"Samurai Commando Mission 1549" released in 2005 is adapted from GI Samurai aka Time Slip 1979 and is a modern day retelling of the original movie