Hi Michael,
Congratulations. Light at the end of the tunnel is a very cool thing.
Yes, marking the bed to frame bolt holes from the bottom is the way I did it too.
I recently did the wood on my 55 first. The Mar-K folks were a huge help to me. They gave me measurements that got things centered and lined up perfectly.
When I traced the bottom of the boards through the cross sill holes, I ended up with 1/2 inch diameter holes marked on them. After removing the boards I drilled up through the center of these marks with a 1/8 inch bit. On the top surface of the boards I measured toward the front of the boards 3/16 inch and based on the Mar-K installation notes drilled a 1/8 to 5/32 inch deep countersink for the offset washers using a 1-9/16 inch Forstner bit. A 1/2 inch hole through the original pilot hole finished the job.
Best of luck and you know if I don't say it someone else will--looking forward to the pics.
