Failed Rocker Arm

Thanks again everyone for the information and replies.

I would definitely agree with Jesse, the fact I cannot get an accurate measurement doesn't help with correct findings on installed spring height. There's really no flat part on the inside of the head casting to take an accurate measurement to.

I'm most definitely leaning towards changing oil & filter, installing a new rocker arm, spinning it over by hand with the valve covers off to ensure everything is moving as it should, and then firing it up and drive on.

My only real concern is if for some reason another rocker goes and I'm not so lucky with the outcome.