The cabin is as done as it is going to get for now; I'm deferring the cowl deck ("boot cowl" if you're a Brit/ Aussie/ Kiwi) so I have better access to layout the controls installation. So onto the "Empennage" or as I call it, the tail cone.

The lumber ripping stage took place earlier on, leaving me with 3/4"x3/4"x10' strips of hemlock for longerons.

Set your cabin on the table and get it PERFECTLY level in pitch and roll. Mark the center of the floor at the firewall and the aftmost cross member. Use a thin thread to make a straight line away from the cabin and right off the end of the table. Suspend the thread with a block so it doesn't touch anything to disturb your coming alignment steps.

This shows the rough longeron sitting on a prop board clamped inside the cabin wall. The other end is on the jig at the same height above the flat & square table.

This is the height adjustment jig; just some boards clamped together with spring clamps. Several things to notice here;
* The square is the elevation control above the table surface. What we're matching here is the height of the bottom edge aligned with the bottom of the upper cabin longeron. The base of the square is barely touching the thread giving perfect alignment with the center of the cabin. You can measure over from the vertical edge of the square to place the longeron in any relation to the cabin center.
* Tape measure is set for proper longeron length: upper longeron so 109" aft of the cabin post
* Guide block keeps the straight edge string from contacting anything
* The tail plate is there just to make it easier to see the guide thread

Use a straight edge (I used some 3/4" scrap stock) touching the inside cabin wall to draw a line on top of the longeron. Make the aft part of the line run off the longeron on the cabin wall side a bit more than 3" behind the forward end of the board to minimize your waste.

To cut the tapers, run a piece of plywood to some width (I used something about 6" but it doesn't really matter) on the tablesaw to square up the cut edge. DON'T move the fence. Next, clamp the cut line very exactly to the edge you just cut on the plywood. Push them both through. Perfectly aligned taper to the cut line you marked in the step above...
Tip: put a scrap 3/4" thick board [matching the longeron thickness] on table, adjacent to the fence so your guide board and longeron stock runs through flat & level. This was my first proof-of-concept pass and I DIDN'T have the "leveling block" in place; you can see the slight angle on the cut in this photo...

This shows the resulting taper fit. I'm happy with this. Note the 3" forward pencil mark shows what gets trimmed off later as excess.

Now to taper and bevel the stern ends. The cabin-end tapers are marked on the 3" line that gets glued inside the cabin. The square replicates the aft-most upright cabin structural post. The upper longeron sits above the square and the lower longeron crosses at the 15 1/4" point as it will later. Spring clamps keep the left & right side members aligned.

This is the "whole table view" of the parts laid out. The vertical fixture allowed marking the forward tapers. The red snake is a water level. Ignore them both for now.

Close-up view of the longerons aft-end in rough position landing on the tail plate, DWG82. Yes, there is some chipping of the top layer of plywood. I figure it's ok as there are 19 other layers in this part.

Top view of the same location. Several details to call out here;
* Shims are inserted to replicate the final spacing between the upper longeron tails. The lower longerons need to be tapered in width to meet the 3/4"-to- 1/2" final dimension. Marking the length of the taper is other purpose of this layout excercise.
* All these parts are in their "square cut" status
* Overlaying a 1/2" strip of spruce on the front of the tail plate allows marking it with bevel lines for final fitting the longerons and the bottom edge
* After the tail plate bevel is cut, the spring plate can slide into position for marking its final bevel cut

I laid out the longerons on an XPS sheet, measured and marked the positions and sliced it up. These photos show the panels with the longerons laying on them and then later that evening glued up and using plywood boards to weight/ clamp the resin into solid contact. I'll add the remaining panel sections after I fine-tune the longeron tails into place on the spring and tail plates.

After the sides epoxy cured, stand them up and confirm proper seam gap at the cabin wall for equal reveal on both sides when the tails are in the position jig. So far so good.

I borrowed neighbour's [Dr. Ken Melvin, M.D., Phd and a whole bunch of other degrees I don't even understand...] laser level to shoot a straight vertical line through the cabin center to the tail. It's [very] slightly out of true but I think I can work that back when I glue the bottom skin on. The top tails center on a 1/2" spacer and you can see how close it is in the upper photo. The lower photo shows the laser beam is centered between the lower tails so that's good.

The bottom skin was cut slightly "too wide" allowing me to perfect the alignment when it gets glued to the side panels.

Now it's on to glassing the interiors of both side panels before joining the bottom skin and locking the structure into alignment...