I have made a max file with all the vehicles & the master chief in, for reference while making a level. As long as you don't link them to the reference frame the models won't get exported with the level so you don't need to delete them to export to .jms.
Just follow the HEK tutorial at the bit when you import the master_chief model. As its in .max format, you have to merge it with the scene (file > merge) instead of trying to import it like a .3ds. You can download the file Here.
Scorpion,Warthog,Banshee & MasterChief Reference Models
it looks like they were objects exported from HMT and imported into max. they dont need to be scaled either(at least not with the maps in spark edit). i know you can export a map from SE and when you import it, it will be the exact size that it normally is. so again i think that HMT does it accurately too.