Before you worry about a fix, determine if you actually have a problem.
First step for you, google "hydraulic lifter preload" and read up. There may be some info on this on rollaclub, but limited. I think I wrote about it once before. Regardless, there is ample info on the net.
Once you understand it, you need to measure up to work out if you have a problem. Generally you should aim for 1.5mm preload. When you read up you wil learn how to measure it. Be advised this is a very finicky process, not difficult but you need to take care on a k motor to fleet accurate values.
It is possible that you won't have enough preload, the solution to this is to shorten your rocker posts commensurate with the difference in preload. For example if you only have 1mm preload, you would shorten the post .5mm to get the 1.5mm desired.
Any machine shop will easily be able to shorten the posts for you.
This is the simplest solution, you might have a lot of trouble finding the exact Length pushrod to suit.
Snot35 makes an interesting point about takeup of the lifter but it's not that straightforward. Lifter preload is the key. Read up you must young padawan.
A12 lifters are for solid conversions. Forget them, you have a hydro cam not a solid one.