1974 D300 360 fresh rebuild will not start

Here's how I would do it, on an engine not bored ;
I Line the dots up; pinch the chain so they can't move, then slide them onto the stumps any old way. With the crank-sprocket engaged with the key,I just turn the cam until the cam-sprocket slides onto the key.
Once the marks are indexed right; it does not matter where the crank is nor where the cam is, as long as the sprockets slide on to the keys and I have NOT allowed the chain to decouple from the sprockets.

After the front cover is on, I can set the damper on the timing tab "TDC" mark, which can only occur with two pistons at TDC; namely 1 and 6. I determine which one is on TDC-compression and stab the distributor in accordingly.
Immediately, if I have not degreed the cam, I check that split-overlap is in the ballpark.
Com'on this is not heart surgery.
Next I bolt the heads on and, and immediately, before the valve gear is installed,I do a LeakDown test. I do it with the pistons on the bottom. This has the additional advantage of proving that the cylinders are not cracked, and since at the bottom is the best chance to have round cylinders, I should get the best readings.
Under the ridge at TDC, is gonna make the worst readings; unfortunately, under the ridge is also where it is most important to capture as much pressure as possible on the compression stroke, cuz the fire has already been lit when the piston gets there, and the pressure is rapidly building towards many times atmospheric.
After the Valve gear is on I do a second LD test, to see how bad the tops of the cylinders are.
If a bunch of it scoots past the rings at or near TDC-Compression,
I got a sick sick engine.