How about using a few TTL gates in series since the output of the oscillator is already TTL? (As you noted, use the osc output to trigger, and instead of driving the TD from the osc output, drive it from the TTL gate chain). If I'm reading the manuals right, I need a 75 ns propagation delay from pretrigger to TD output. That's not hard to do with 7404 hex inverters, from the datasheet per gate typ 12/max 22 ns rising and 8/15 falling. The only flaw I see is that the 50/50 symmetry of the output would change a little.
I have many GR adapters to a variety of connectors, some of which I've never seen before. But only one tee and no splitter. Any idea where I could find one? (needle in haystack, or maybe unicorn)...
