I disagree with your need to use the older chain design. The valvetrain has very little resistance on it when assembled properly. During some other engine assemblies, I've come across a couple of possabilities that could have put undue strain on the chains...
While assembling one long block, I got interrupted while tightening the tensioners and cam caps. Long story short... I released the clip from the chain tensioner before tightening the caps down totaly to spec. I started to tighten down the caps, then realized my mistake and had to go back to correct it by removing the tensioner and retiming the cams once again. Is it possible you removed the clip from the tensioner and allowed the chains to have tension before finishing the cam caps?
Another idea I had was if you changed the orientation of any one cap... They need to be marked and returned to the same place they came from as each cap is machined to it's own individual spec and will put a lot of friction on the cams if torqued down on the wrong bearing base.
If the wrong lash cap was used it would throw the cam alignment off causing the chain to run crocked between the chain gears.
