With the basic car built, we need to look at the side sills. This is the most complicated part of the conversion, but it also gives me the opportunity to try some new skills.
Looking at the side sill casting itself, it's not a very complicated part. There are some rivets, and holes for the grab irons and stake pockets. The fact that the stake pockets are separate parts has a huge impact on being able to modify this model, as we'll see in a moment.
But the first thing we need to consider is how to make the longer side sills.
Option 1: Extend at either end.
This creates a much longer space between the first stake pocket and the end of the car. But the bigger issue is that the rivets for the bolster are out of line. We could consider moving these rivets, but the extended space between the end and the stake pockets will be noticeable.
Option 2: Extend from the middle.
Just like the deck, we could cut the side sills in the middle, and extend it that way. Since we didn't alter the relationship of the bolster from the end of the car, that takes care of that issue. But the relationship of the rivets for the crossbearers and crossties don't match, and it makes the spacing between the two center stake pockets noticeably too wide.
Option 3: Make multiple cuts.
This is a possibility I considered. But the stake pockets are almost evenly spaced (within 1/2" in most cases), so this requires a lot of little cuts.
Option 4: Scratchbuild the sides.
This is both easier, and perhaps a bit harder, than it seems. But it will also allow us to get the proper look. So that's what I've done.
I found that some .040" x .125" strip styrene was a good match for the basic dimensions of the model's side sill. It's just a matter of cutting it to size.
This is the larger of the new side sills compared to the original.
Then I needed to lay out the stake pockets. Starting with the CP car, I used the drawing for the CP car for guidance (since they are similar lengths. The center line for my car (yours might be slightly different due to cutting and sanding differences) was 2.8610 on my digital calipers. To the first stake pocket, 17" from the center line, is .1915".
Now the next several stake pockets aren't precisely even. To the next one over it's 3'-5", then 3'-4 1/2", then 3'-4 3/4". Because I knew there was going to be some variance simply due to my ability to precisely align everything, I stuck with one measurement of .4707" for all three. The next pocket is spaced closer 2-3/4" closer than the widest spacing. Since this was the shortest span, I opted to measure from the end to the first stake pocket, .2300", and used the wide spacing of .4707" between the first and second pockets from the end. That made the remaining spacing noticeably closer, as it should be.
Once I had them all marked, I carried those marks over to the second side sill. I then flipped that so I could carry the marks to the other half of both sills. Now I had the stake pocket center lines marked along both side sills.
I tacked the two pieces together back-to-back with CA. I carried the center line mark across the top edge. Using this as a guide, I used the model sill as a drilling template by lining up the center line to the center of the stake pocket location on the original piece. I then drilled all the way through the model sill and both side sills.
For the T&P car, which is only 1 board longer than the CP car, I had no drawing to identify the stake pocket placement. So I tacked the completed sill for the CP car flush to one end, and drilled out the stake pockets to the center line. I then tacked it to the other end, and drilled the other half.
This means that for the T&P car, I used the same spacing as the CP car, except a slightly wider spacing between the two center stake pockets, which happens to be a pretty close match to the center spacing of the NC&StL car.
In these pictures, the three pairs of side sills are aligned at the center line.
Here they are aligned flush to the end.
You'll note that my hole drilling skills are inconsistent at best. That's OK, this will help align them, and if I find one is too far off, I'll just get rid of the locating pins. Since the stake pockets and side sills are styrene, the pins aren't really necessary.
Here's are the three length sides with stake pockets installed.
You can see how the stake pockets highlight the differences in the sides. As it turned out, for the pocket locations that were mis-drilled, it was easy enough to just squash down the mounting pins since they are very small. In fact, when gluing styrene pockets to a scratchbuilt styrene side in the future, I probably won't bother trying to drill the holes. It just didn't provide a significant benefit.
And here are the sides installed on the car bodies.
On the car built as designed on the left, there is a single gap that will be filled by the installation of the coupler pocket. The car on the right has Kadee pockets, so I have a gap on either side of the bolster to fill. Also to come - rivets, end sills, brake appliances, and other finishing details.