3.9 v8 dizzy nightmare!! HELP!!

The story so far.
Decided to service my disco and for good measure change the rotor arm and dizzy cap.
At the spares shop they were unsure about which rotor are i needed so i nipped out and removed mine to show them. (The Arm was stiff to pull off). Bought my bits and refitted the original rotor arm.
Vehicle will now not start.
The roter arm has 90 degrees of play in it now!!! i have heard that it should have a spring loaded mech inside the distributor and the rotor arm should beable to be moved and then spring back to it original position? Mine does not so i assume i have broken mine pulling the rotor arm off!!
I have ordered a replacement distributor but how will i know the correct position of the old one to refit the new one in the same place?
Any help / comments will be greatfully received.

Andy

B4 I bought a new dizzy would have wanted to figure out where the play was coming from? Basically u line it up roughyt using the timing marks then use a timing light to get it exactly right. Probably some computer gizmo nowadays but thats the way I used to do it when I was a lad......

Hi
Thanks for that.
I've been having a read and see i have got to put the enging at 6 deg BTDC ( i'm presuming this means Before top dead centre) then fit the dizzy with the rotor pointing at number one lead.
What markings are there to tell me when i'm at 6 dec BTDC?

Andy

This could take a while couldn't it? Have u checked on the crankshaft pully? Thats wot I used to use when I used ta play. but ........

I've heard the timing marks are on the crank shaft vibration damper?? can anyone post a picture of explain where it is??

Cheers

Do u know where the crankshaft is - could be a good place to start looking

are you sure you have located the rotor arm properly and its not that what is giving you all the play!