I strongly believe the original machine is pure random and that payout percentage is controlled by number of holds given, nudge feature frequency and the number of nudges available.
I would make a function to always nudge in the best result (people knew these reel bands off by heart) so not an unrealistic thing to do.
Then start with a hit rate for nudges (say 1 in 50 games) as a starting point.
Start with awarding the number of nudges on a totally random basis 1 to 10.
With the above you should be able to get to the percentage you want be altering those variables.
I would look at the holds last. This will make a difference but getting the percentage about right before is what i would target.