So this is just uninsulated pipe you have? If so, I wouldn't use it. 5/8" Kitek is going to be almost impossible to find fittings for. It wouldn't cost that much to just replace it with 3/4"pex.
You only mentioned the 5/8". Are all 4 pipes that size or are two of them larger?
Also, since this is Kitek pipe, (made in Canada by IPEX) I would check it over real good if you use it. They had a problem with the inside layer de-laminating from the aluminum and bulging inwards blocking off a lot of the water flow.