Yes it is a pain to get the spacer right You need to make sure the roller tip is centered on the valve tip , I usually use lash caps to increase the surface area & protect the valve tip , you want a little side play , .010 or so for heat expansion , & you can move the roller tip over slightly if the pushrod is too close to the casting of the intake port .
To get the right pushrod length you have to be sure the lifter is on the back side of the lobe so as low as possible you want the adjuster set as high as possible then turn it down 2 full turns , put a feeler gauge in place for lash & measure the total distance left between the lifter & rocker , if this is using a solid lifter !
With hyd you need to preload the lifter so I would start with the adjuster 1 turn down from topped out'
I would order pushrods from Smith Bros in Bend OR , great service & fast .