Flat tappet to solid roller...

FYI I tested the welded pushrods strength using press and applying vertical force on them... It took 3.5 tons to bend them, first the ball part on the bottom flattened and started cracking at just over 2.5 tons, then pushrod bent in the middle. Welded part was not affected at all by applied force.
I would not risk using them anyway. Also please have in mind that weld was made by skilled tig welder.