Ok well there are 2 main things that you have to do to make a basic spump:
1)Make a pump handle/rod system
If you do those 2 things you will create an open bolt pump. Number one can be done a few ways but it basically all involves making/getting a pump handle and attaching it to the bolt with a pump rod. Number 2 can only be done one way which is by replacing the valve pin with one without a blowback slot, either by getting a valve pin from either a t1 or a trilogy cocker or by using some jb weld on the stock valve pin. Most people opt for the jb weld on the valve pin.
If you want to go all the way with this then you can make it a closed bolt pump by doing a simple modification to the hammer. The involves cutting a slot in the hammer from where the bolt pin hole is all the way to the front of the hammer this allows the pump handle and bolt to return forward before the gun is fired.
This is probably the best tutorial you'll find on how to do the conversion
There is one small modification I would suggest to his mod though. Halfback the gun and run the back block like a halfblock cocker, that will allow you to lose some of the weight and end up with an extremely clean looking marker.
And remember a a piranha is a spyder is a spyder clone any information you find for one will generally work for every other one.