Question: Adding a verical plane to a plot

Using spacecurve I've created a diagram of two curves in space, they are reflections in the plane x=y (in this diagram they are labeled k[a1]=k[a2]). How can I add the plane to the diagram?

My intuition is to use 3dplot, and then combine them with display. The problem with that is that 3d plot wants a function of the form z=f(x,y) rather than x=y.

(here is the code for the diagram)

spacecurve({[(5*10^(-4)*100)/C[T], 100*10^(-3)/C[T], C[T]], [100*10^(-3)/C[T], (5*10^(-4)*100)/C[T], C[T]]}, C[T] = 10 .. 100, labelfont = [TIMES, 32], axesfont = [TIMES, 32], titlefont = [TIMES, 32], captionfont = [TIMES, 32], labels = [conjugate(k)[a1], conjugate(k)[a2], conjugate(C)[T]], tickmarks = [[0.1e-2 = k[a1], 5*10^(-3) = 5*k[a1], 10^(-2) = 10*k[a1]], [0.1e-2 = k[a1], 5*10^(-3) = 5*k[a1], 10^(-2) = 10*k[a1]], [0 = 0, 10 = (1/10)*C[T], 50 = (1/2)*C[T], 100 = C[T]]], view = [0 .. 0.1e-1, 0 .. 0.1e-1, 0 .. 100])