I would go 3/8 feed and return if you have to replace them anyway. On the return you could get away with the original 1/4 size or step it up to the original feed size of 5/16.
Summitracing sells some good kits and the required AN fittings if you are going that way.
I'm not going to tinker with just replacing the feed. I'm pretty sure both lines are not in the best shape. I think 3/8ths feed and return will work just fine. Now I just have to measure how much I need.
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