Looks like our skis have had similar owners in similar condition, yes the fuel lines are bad mine are in terrible condition and solid as a rock so it will take you some time to get the swing of things, developing a process of your own on the best way to remove them.
Good quality picks I used to remove the stubborn lines and clamps, also really a good tool to have in your collection as well.
For me, I would use a heat gun to soften the hardened line and then use a
good quality pick to lift it up past the nipple without tearing it up and pull the line off. I bought 1/4 automotive fuel line from amazon 25ft spool for only 20 bucks.
To get those awful clamps off just use your pick or small enough flat head in the little hole and (what I did) just move it left to right and it would pop right off.
I would replace your fuel strainer and fuel selector valve along with a good carb cleaning too. My carb is very corroded and the PO
tried to mend its issues but stripped out a screw in the process so I am trying to resolve this issue. But OEM kits are the only way to go.
(currently in the carb rebuild process of semi-resto for the craft)
My spring was corroded too and the oem kit comes with 3 (based off of what pop-off pressure is needed for your setup.) As of right now the kit I ordered sbn 38/44, is $40 USD.
(I knew I was replacing it so I wasn't all that careful with it but the picture is a good example of what happens when you have those lines)
You will also need to flush out the bad oil that is in your ski too (PO used wrong oil tcw-30)
I used a siphon from harbor freight and sucked up the majority of oil and all the bad gas in my tank, was a good buy actually if you do not have one.
You and me seem to be in the same situation and this forum is an amazing place to get information and helpful tips.