Trans and shaft swap. Am i on crack?

My 65 Dart was small block, 727, with an 8 3/4. Trying to shave a little time off it I swapped in a 904 that i prepped for bracket racing. I had a new drive shaft made.
Now I have 727 and a drive shaft sitting around. My 70ish dart is a 340 4 speed that I want to put the 727 in so I can let my daughter bracket race it.
My question here is both darts have the same wheel base, use the same frame rails, and 8 3/4. If I put the 727 in it, in theory the drive shaft should work on my 70ish. Whats your thoughts?