The Motobecane Track frame is the same as the Fuji Classic and the Windsor The Hour.

Get new pedals, clips, and straps. MKS GR9s and Sylvans are reasonable choices that won't break the budget. That was probably the best upgrade I made to my Motobecane. Also consider a front brake, new saddle, and bars. You can do all this with some pretty solid parts for under $150, which would still put the total cost of your build way under your $600 budget.