There are three basic methods of drawboring that I am aware of:

1. Layout on the horses and bore as part of joint cutting process. Pros are efficiency of effort. Cons are the absolute lack of fault tolerance.

2. Tim's method of assemble on the deck, prick offset center, disassemble, drill and reassemble and drive pegs. Pros are easy control of frame dimensions with fault tolerance. Cons are related to efficiency ideals.

3. Point to the joint drilling. The mortised member is predrilled, The frame is assembled and strapped tight, the bore is drilled with slope. Wild card method, not consistent for me to endorse.