Partial fix, they're functional but some usability/info is missing:
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GUI Issues (on old ships):
# Power bar is not visible, the power consumption consumption is still being displayed at the top though. The power aux bar is visible (if you have power aux) so that works.
# new build mode panel shows new reactor stats on old ships
{F23621}
{F23623}
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Functionality (on old ships):
# Can't activate/toggle defensive effects
# Can't activate/toggle power aux
# Can't activate/toggle jump drive computer (old one)
# Jump inhibitor (old one) does not appear in the weapons menu after you made it, possibly can't use it either if it was there.