Reset inits the L port to input, and makes SK output the CPU clock. The Entex Space Invader game sets the L port and SK to outputs, so when I let it run and then went into ROM dump mode (SO=3V, SI=gnd), it started dumping the ROM contents at whatever address the program counter had.
If the game didn't set the L port to all outputs, I would have had to do the forced instruction setup to do that. Because the game uses it as an output, I did lose the SK sync, but that was no big deal; I just looked for edges and sampled in the middle.
When I went from reset directly to ROM dump mode, I got what you got- a clock on SK, but nothing on L.
Since I was able to figure out where the ROM dump started, I didn't try to force instructions.
If your chip should be setting L to output, try tweaking the voltage on SO a bit. I had to adjust it depending on VCC I used.