New Cam Chain - How Tight ?

So, I'm just assembling the top end of my '73 Z1 engine. However, after putting the cams in, the new DID cam chain seems very tight even though I haven't put the tensioner on yet. If I push the back of the tensioner arm there is no play at all.
My first thought was that I must have the cam timing wrong, but I've done it three times now with the same result.  I have then crankshaft set to the 1/4 T mark and I'm counting the links from the pin above the exhaust camshaft sprocket mark and the inlet cam is on the 28th pin. The end lobes of both camshafts are perfectly level with each other and the head surface. I have a notch in the end of the exhaust cam on the right side and the notch is perfectly level with the head as well.
I do have reasonable slack in the middle of the chain between the cams, but as soon as I tighten down the top idler it gets tight. The top idler is a stock Z1 one but with new top and bottom rubber blocks.
I can turn the engine over with some resistance, but if I slacken off the bolts of the top idler, it definitely frees up some.
 

Sounds like you have the marks and pin count correct. The chain will be tight but there should be enough play to install the center sprocket. Once the sprocket is on you can reach in the adjuster hole and push on that chain. It  will have little if no movement. I would not rotate the engine without the cam chain tensioner in place. Might be too late now but i'm a big fan of replacing all those 50 year old idler sprockets. I generally replace them with Liska units.

Thanks for your reply.
Yes, when I tension down the top idler pulley fully and then reach into the tensioner hole and push on the chain, there is no movement at all.
I guess that's how new chains are until they wear in a bit ?

If you're having a hard time, DON'T force it. Something is a-miss. Sometimes the 122link chain can get bunched-up around the crankshaft sprocket, double check that first!