I purchased new bilstein shocks and struts for my project 914. Instructions state not to use the bump stops on the front struts.

My rear shocks as installed (KYB) did not have any bumpers.
Decided to go with coilovers on the back and ordered the groundcontrol setup after
watching Ian Karr's excellent video. In his vid, he cut the stops down as per instructions.

I don't have them, (well, unless I tear into another car) Do I really need them? If I do, where can I source them?

The bump stops prevent the shock from bottoming out, which would destroy the shock. They usually come in 3 segments and can be cut down if needed.

You can work out how much bump stop you need by marking the shaft when it is all the way pressed into the shock (before installing). Once installed, you can cut down the bump stop to be just enough to cover your marking on the shaft (plus a bit of extra). That gives you maximum travel but still prevents the shock from bottoming out.

I agree with andy

You can likely get by without if the ground clearance is stock

But if the car is lowered or likely to bottom out you will eventually blow the shock

On the fronts I am using 911 bilstein. Specs state bump stop is internal. No specks came with the rears...Ok where is the best place to buy?

WTB on world, 914rubber, and many other places sell the rubber pieces.

Found some from URO...for vw, but wait. At least the back of the car is vw...right?
Look identical to stock 914, just a different color. We'll see in a few days.