Rebuilding heater box, replace core?

I ran into this same problem. The new unit interferes and started to crack the box. I got a quote to record my old for $240. I thought that was very high but I don’t have much choice at the point.
Well its more than I paid but lots of factors that could effect pricing. Overhead, source of cores, erally setup to do the work vs an interuption to normal business.
Might shop around if there is any other places in reasonable driving distance.