Paul,
I've been involved in designing and erecting several large timber frames, and
dismantling a few more, and I'll pass along a few things in response to your
questions.
Jowled posts, or gunstock posts, and they are sometimes called,  were ripped
from full-width timbers.  I'm not sure you could replicate the strength with
any other arrangement. I did a mess of these from 8 x 14 oak timbers, 14 feet
long. All but the top 3 feet had to be ripped off as waste. After doing a few,
it became obvious that there had to be a faster way.
What we finally decided on was to crosscut every few inches along the waste,
then knock off the resulting blocks with a big mallet, and or a framing
chisel. The raw edge was then finished with drawknife, slick,  and planes. In
green stuff,  this is easier than it sounds.
I would NOT use metallic fastners in any timber frame construction for the
reason that humid air will deposit dew on the metal, and draw it into the wood
structure right at all the critical joints, thereby causing it to deteriorate
long before its time.  The same applies to bolted-on joint braces, nails,
throughbolting, and screws. This admixture of two disparate building
disciplines is, in my opinion, the cause of the early demise of a lot of this
country's covered bridges. I believe the speed of decay is related to the wood
species,  but it will surely take place in time. An all wood joint will last
centuries.

Trenails, or pins,  are most easily made from very dry stock, ripped in long
lengths,  and planed from the square to a slightly oversized octagon shape. A
simple jig helps with the planing. Make it up in the same fashion as the jig
used for planing the segments for bamboo fishing rod blanks. Arrange it so the
corner to be planed just sticks up proud of the jig walls, and you'll know
you've planed deeply enough when your plane begins to strike the sides of the
jig. Use a block plane or a small smoother set fairly coarse. They can be
rough cut before driving, and then trimmed, or they can be finished on the
endgrain with more detail, then driven. The idea is to get the corners to bite
into the wood of the timbers, and then have them swell as they wick moisture
from the less-dry timbers. The bore circle of the drill bit you use should
just fit into the octagon that describes the pins you're making. This insures
the corners will bite when driven. Most of the ones I've extracted from
buildings I've torn down were handmade like this from black locust (robinia
pseudoacacia) or honeylocust. (gleditsia triacanthos)  The stock for these
cannot be too dry.

For larger structures, it is helpful to bore holes so that they are slightly
offcenter from each other. The driving in of the pin or trenail then pulls the
joint tight. I've seen this referred to as "drawboring",  but the term itself
is confusing.  The practice itself is useful however, as I've seen the
endgrain of the girt or horizontal member actually forced into the side grain
of the post by this technique.

I'll leave you in the hands of our other timberframers,  who I'm certain are
lurking somewhere near.  Good luck, and DO supply pictures when you're done!
Regards,
Nick