Installing cartr.:slide it all the way to front?

The position of the cartridge determines the overhang, Overhang :^).

If you have a tool to check your set up, you need to acquire one.

It matters much. If you don't have the tools to setup a TT properly you need them. It is not an easy process. If not setup properly you will get less than optimal sound and probably damage your vinyl.

Your arm or turntable manual should tell what the overhang should be. This will hold you over until you get an alignment device of some kind. Overhang should be measured form pivot to stylus tip.

Wow, how can you call yourself Overhang and not know about overhang? Seems kinda odd, no?

Hi Overhang,

The overhang for the Rega 600 is 15mm. That is, your Shelter should be mounted on the Rega where stylus would extend 15mm past the center the spindle on line with the pivot (center mount). Unless the mount of your Rega is loosened, she might not travel that far.
Another way to go at it is the effective length. This is the distance between the pivot and the stylus. It should be 237mm.
But this is just the beginning ... dialing in a cart is part craft and part art. Sometimes dispensing with tools and trusting your ears can bring benefits, as well. So roll up your sleeves, do some research, download some protractors buy a Shure stylus force gauge and lift up your heart for all will come right!