The best lot for biking depends on which part of Safe Harbor you are climbing. For access to South you can park at the Colemanville Church Rd, Conestoga, PA 17516. Head onto the gravel trail and make a right (North West)
For access to Safe Harbor North, consider parking at the Turkey Hill Overlook Trail, 2501 River Rd, Conestoga, PA 17516.
And for the hike-a-bike options... For South: Park on Powerhouse Rd and hike it up - this gives great access to the Cemetery/Dam wall at North as well.
One can also park at The Shenks Ferry Wildflower Preserve: 857 Green Hill Rd S, Conestoga, PA 17516, this puts you close to the 'Key West' sector of Safe Harbor South.
I can answer any more questions, I am right down the road from the place