Just picked this beauty up from a local friend. 512 in sanitronic colors. Original boxes attachments and manuals! I am very excited to polish this baby up!
If it had a the original armature, it should still have a close to original sound even with a lexan in it. If it's a newer armature, the lexan will make the Kirby sound like a Heritage II
Don't fret over the plastic fan. It has 11 blades instead of 6 and is lighter so it will give you more airflow. It is made of a material called Amodel not Lexan. Amodel has many of the same properties as Kevlar and is just as strong as the original metal fan.
It reminds me of when I found my 516 in a thrift shop, complete with all the attachments, boxes, paperwork, etc. the only things not original on it are the bag and cord. They match though so it not that big of a deal to me.