OK - let's work backwards on this...stick a metal object like a screwdriver blade into a spark plug wire. Hold it close to the block while a friend hits the starter. Spark? (Should be a strong, blue one....) If you get a spark, timing is the only issue.
No spark and I'd think that the points are shorting (the little plastic insulator is fiddly if you haven't done it a dozen or more times....) or the condensor could be bad. I've had a new one be bad right out of the box....
Take the top of the dizzy off and remove the rotor. Use a non-conductive tool on the point's spring to open 'em. Spark upon opening? If there's no spark here, there won't be any to be 'amplified' by the coil....
You've got TDC established, right? But since you swapped the 24v dizzy for a 12 volt one, the drive gear adapter - the steel donut - may not be part of the picture. When everything is set up correctly and #1 cylinder is at TDC, the rotor should be pointing to 1 o'clock and cylinder #1....
Cheers