I think that would work fine, with the same signal quality as before. There is no need for symmetry but if you insist you might add a flip-flop in the final stage. Actually most fast pulsers produce just a short pulse starting with the performance-specified edge. A 74121 as final stage could be used to limit pulse duration.
BTW how do you drive the TD from a TTL output? With 7404 the source current I-out-high (0.4 mA) is probably insufficient. Do you feed the TD from the cathode side? I mean with TD-anode connected to TTL-plus and TTL-plus connected to scope-GND? That way you can profit from the larger sink current I-out-low.
Albert
