I seem to recall discussions on MVS about people making the tool. It appears from what photos I've seen that the slots on each cam need to be in line with each other - if so that would kinda make a home-fab tool possible. It would be important for the tool to be a close tolerance fit in the cam slots. I wonder if the cam slots are a bit off center so that you don't get a cam 180 off??

What about this? You use a dial indicator in cylinder #1 to find true TDC - that would null any questions about where the crank sprocket timing mark really is. That was the biggest problem I had when replacing the T-belt on my white block. It's rather vague.

Then use a cam hold tool on the LH ends (either purchased or home made) to assure both cams are at TDC.

Loosen the sprocket bolts on both cams.

Install the belt and apply tension.

Assuming everything is still at TDC at that point, THEN tighten the sprocket bolts.

This is all just me thinking - someone else may read it and blow holes in it.

I still have a question in my mind about what keeps you from having one of the cams 180 out of whack. Doubtful if the cam that drives the distributor is 180 out as you had spark enough to get it running, albeit rough. If you think about it you could have a cam 180 off and still not experience piston/valve interferrence as the piston would still be in the same position at valve openning that it should be, just on the wrong stroke. If you could see the index mark on both cam sprockets you would know that you aren't 180 out as there are 3 bolts (odd number) in the sprocket so it would be impossible to be wrong. Have you looked at the sprockets very very close? I found those marks to be a very faint score on the sprocket face.