I only had the ratchet straps as well...Bit of a pain they are...I had a ratchet strap stupidly put on the bottom to hold the 2 side straps from slipping off, and in the middle of sliding the motor out, realized the ratchet wouldn't clear the frame. I had to remove that one and keep working the motor out. SO...for future reference, you might get away without the bottom straps, but I won't recommend it!!
OK just checked you post, Mark, looks like you didn't bother with the bottom one either. I guess if you make good and sure they can't slip, you're fine.