Erick,
Unfortunately I don't have a Silverado with the LF motor to compare the length at the end of the bag chamber. I did go and check my Ultralux Classics, and I see what you mean by how far back the motor sits in it as compared to the Silverado and SJ. Too bad most of these weren't sold in Canada. So, this little boy went to the lux service manuals, here are the part numbers listed for the bag chambers Olympia 41961, Silverado 43114, all 1521 models 42841.
We just might have to nominate you for the Nobel Prize in vacuum cleaner engineering and design!!
Vernon