I have my slab glued up and had to cut the rough shape with a jigsaw. I have a template for my router to true up the bottom half of the form, but I am not sure what to do about the upper half. Unfortunately, given that I couldn't use a bandsaw, the cut isn't perfectly perpendicular, which isn't a problem for the bottom half once I route it with the flush trim bit.

What is normally done to the upper half to get it squared, trued, and flush?

The bandsaw usually does it good enough by default. But in your case, why not make a pattern for the top and use the router bit for it too? Wouldn't take too long.

I get my upper form rough out and then mount the hardware to the forms, then I draw my lines about 1" gap between forms for a recurve, 1-14" for R/D longbow.
I use the band saw and the round end of the edge sander to finish it