Maybe. But when he was in preproduction in England he bought all this expensive video equipment that he used to do tape-to-tape video editing using old war films that he used to show people and ILM guys how the scenes would cut together, for both the "here they come" sequence and the end battle.

Then when he was in Tunisia someone broke into the house he was renting and stole all the video equipment. I don't think the tapes he made have ever been publically seen, its possible that they don't exist anymore for one reason or another. Maybe he did like what I did for Return of the Jedi in 1989 and recorded Super Dave Osbourne over it. :p

But yes, maybe they were able to get 35mm prints to use for the workprint. Also, the workprint is black and white for all footage, including the live action original footage which obviously was filmed in colour. It was all printed to black and white for editorial use because it was cheaper, so probably 633 Squad would have been too.