Do you have your rocker boxes off the engine? If so, put grease in the little cups at the ends of the push rods. That way when you drop the rod down the push rod tube you can feel it stick to the top of the tappit. You'll know it's on the tappit because when you pull up on the push rod you can feel it try to lift the tappit.
The rocker box gasket comes with two small holes to fit over the push rods and they will keep the rods lined up with the rocker arms. I back off the rocker adjuster so I can gently feel if the ball on the other end of rocker has seated into the grease in the top of the push rod.
If you feel you're sure the rockers are properly seated on the push rods, take up most of the slack in the rocker adjuster and turn the engine over a few times to get most of the grease out of the cups before adjusting the valves.
Before doing any of the above be sure to flatten the bottom of the rocker boxes on a flat surface like a cast iron table saw top with some 220 grit sand paper attached to it. Also, use a good quality rocker box gasket. Most people like the gasket that is a combined metal and fiber gasket provided to retail Triumph parts companies by a supplier that I think is called Coventry Spares. Coventry only sells to retailers.
I hope all this makes sence to you and others may chime in with their way of getting the job done. Good luck with your project!....Gary