Large cross of: sim[D]/Tm6b,Tb x Espl[D]/Tm6b,Tb
take non-Tb progeny and cross to double balanced 3rd (e.g. Tm3/Tm6)
Cross individual F2s to double-balancer on 3rd. Expand these single fly lines (1 generation should be enough). PCR across the deletions to screen for double mutants.