does any one have any advice on changing the track out and susppension out for something quite longer not the normal 136 conversion but anything longer

How deep lug do you want?
If you want to go 144 or longer, you'll have to do something with the cooling. Also the stock tunnel strip coolers needs to have a notched track.

Should be no problem swapping the xtra-10 skid out for somethiong longer, you'l just have to move the mounting plates in the tunnel.

I'm thinking that if you are wanting to go any longer than 144 and you currently have a 121 that you are going to have to get a longer skid frame from an RMK first.

You would then have to notch the track based on how long of a paddle your going to run. Once you get past about 1.5 your gonna want to notch the track, and anything bigger than a 2 is gonna require a set of smaller drivers or a drop and rolled chain case or both.