Bit of a delay in replying...one thing to do if you haven't already started, is draw around where the old one is so you know where the new ones supposed to go.
That's how i welded mine back on (just matched the number of spots to new holes)
While i was at it though i pretty much welded up any areas the new and old panel lined up lol.
A fancy spot drill will deffo speed things up. I had a normal drill, a grinder, a few hammers, a chisel and the mega drill. It still took ages to defeat lol.