Yeah, best re-do it to double check, but your theory is sound. A DTI gauge on top of a pole through the plug hole and get it at the top of the stroke, trying to guess the true TDC due to the dwell period at the top. You'll never get it 100% but very very close.
It's been a LONG LONG time since i did any MS1 setup, but I think what I'd do is:
set the fixed angle to 10 degrees (not -10) which will make the spark spark only at 10 degrees regardless of what the spark table says. Check cranking is set to 10 degrees as well as I'm not sure if that over-rides the fixed angle.
The crank it. I'd remove the injector supply (don't try to start at this point), or just remove them from the inlet but leave them hooked up to watch them spray petrol everywhere.
Once you verified they are all squirting, remove the supply so they don't fire any more. Then remove the plugs from the block so you get no compression (easy cranking), but leave the plugs on the block. You can verify they all spark, and still use the timing strobe while cranking then.
Crank, and set the strobe to 10 degrees. It should match up perfectly with your new marks.
Only when you know you have accurate timing, can you check everything else. If 10 degrees works, change the cranking and fixed to other values (15, 20, 25) and verify that they are accurate as well.
If it's out slightly, adjust the trigger angle to bring it in line
That's a start anyways. Log it all as well. You will probably have a higher than normal crank speed as the plug will be out.
If you suspect a VR issue. Log it in first gear while being towed, see how the RPM gauge goes and what RPM you can reach. Again, i'd disconnect the coild and injectors when doing this, but leave the plugs in to assist you with breaking
Krisitan