Probably the safest way is to use a small flat-edged needle file, but in the past I've also used a Dremel cutting disc and a craft knife - which one you choose depends on your confidence (and a steady hand 😀 ). It's also a good idea to slip a thin piece of u-shaped plastic or card into the slot to protect the metal connectors from damage, and obviously to clean up well afterwards.

EDIT: Reread the OP and as cyclone3D says below, alter the slot rather than the card (which is what I was referring to in my post)

Usually people just open up the end of the slot instead of butchering the card to make it fit in a shorter slot.

another option ive used is a flat head screwdriver heated up and just melt the back of the connector

There's the really safe way, and the moderately safe way.

The best and safest way is not to cut the slot and use a PCIe riser/extension. Of course, securing in in your motherboard and having access to all the graphics card ports may then be an issue .

For hard modding, I've done this twice, once just to open up the end, and once to open up the middle of a PCI-e slot in a Dell server that Dell *really* didn't want you to use for graphics cards.

For the end I would use a dremel disc, but by slowly shaving bits off the end by using the disk head on, instead of along the slot.

Also had luck going into a pound shop and buying a mini box cutter - just the right size for pressing down inside the slot without destroying the contacts.

There are a few 8x cards, The GT730 (GDDR5/64b), GT730/GT630V2 rebadge (DDR3/64b) - but not the 128 bit model (Fermi GT430 rebadge) - not sure if they all only implement the 8x length, but mine does

What's the point of doing this? PCIE Express can work with reduced lanes by itself. And electrically x16 PCIE card can work on x8, x4 or x1. This is required by the spec and part of the compliance tests. Some mobile, power-aware PCIE card would even re-negotiate the link down to x1 to save power during idle and low bus utilization.

cyclone3d wrote:

Usually people just open up the end of the slot instead of butchering the card to make it fit in a shorter slot.

This is the easiest way to plug an electrically x16 PCIE card into a mechanically x8, x4 or x1 slot. No need to fiddle with the metal contacts on the card or the slot.

Typically, PCIE port closest to the CPU will be made into a mechanically x16 slot, even though there is not enough electrical lanes to make it a full x16 electrically. This is the fastest PCIE port for GPU due to less hops between CPU and GPU. Even a x1 or x4 GPU should be using this slot for best performance. It is strange that your old motherboard does not even have a single x16 slot.