A credible machine shop would know that straightening a cylinder ram takes time. It can only be moved a few thousands at a time and held in that position, sometimes for up to twelve hours depending on the diameter, before moving it further. Back in the 60"s and 70"s I had the opportunity to have worked in a shop that repaired everything except the crack of dawn, and we straightened a lot of hydraulic cylinder rams. Big ones, small ones, short and long. We did some that local heavy duty shops had tried and failed. It just takes time.
Never had an issue with piston retainment that I can recall.
A point of interest: when I left the business our shop rate was $12.50 per hour and no fancy add on"s like "shop supplies" either.