Just want to know if i should use my ll203 amp in am or ssb mode when running with a cobra CB radio?

Use the AM Mode
The SSB Mode only engages the delay for the relay.

What radio?? Does it have single side band(SSB)? If not, then don't use SSB.

AM - amplitude modulation
SSB - single side band.

If you have SSB, there would be a switch on it to transmit in SSB. If not, it is AM only.

Second, Has this radio been worked on to be able to run on an amp? If not, you will blow the amp.

A CB radio transmits dead keys with 4 watts of power, and transmits with 4 watts of audio.

a 4 watt dead key is too much for a linear amp. You will smoke the transistors. Also, 4 watts of audio is not enough to drive it properly. You won't get full power.

The dead key needs to be around 2 to 2 -1/2 watts,or what ever makes the linear dead key half its peak wattage., and the modulation (audio) turned up all the way.

It doesn't sound like you know too much about CB radio's. Not a big deal, you can learn. For right now you may want to take it to a cb shop and tell them you want a peak and tune, and set up to run a linear.

You can find CB shops usually at truck stops. Some area's they are other places. Check the internet for local shops.