Personally, I think you have got to the bottom of what has happened, saying the pushrod was sat 'on' rather than 'in' the follower cup.
Two weeks ago I had my cam 'faced up' and fitted new followers (all S.R.M.) in mine. After fitting the rods, I nip the rocker box up and leaving a big tappet gap start fiddling with them. Spin them, lift them, and see if I can feel them trying to leave the follower cups, and then centralise as they fall down again.
Anyway, on to you........This time, as I spun the engine there was an almighty clank, and it was indeed a pushrod finding its own way off the edge and into the cup while under pressure. The noise was a valve slamming shut. I've clocked up a few hundred miles since, and all is well after checking everything three or four times on assembly.
Amongst all the advice, Muskrats is as good as any.....DON'T RUSH!.....Get on with it by all means, but reaching a point like tightening the rocker box for the last time calls for a brew, a ciggie and several checks to see all is well beforehand.
As for the followers themselves!.........What a disgrace!....In the past I've gone without food to buy S.R.M parts rather than go cheap, and I'd do it again if I had to in a heartbeat.