By straight shift , do you mean , manual transmission ?
I'm sure that this is OK , but you should check and see if you can download an owners manual online for confirmation.
May have to have trans in neutral too.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.