In checking the pictures I've received (Thank you) and looking at the loco and holding the pilot up to it, I think that possibly, I can grind about a quarter of an inch of the narrow bottom flange from the side of the pilot and not have to take the whole bottom off so as to preserve the original look as much as possible. I've also come to the conclusion that it might be better to have a donor shell to practice on, especially as mine has a bent place under the engineer's "ladder." Can you carefully tap the bent spot back into line with a brass hammer without the Zamac breaking or leave it alone?
I think that moving the front wheels back about an eighth of an inch might give more clearance as well. Can you take one wheel off without a puller?
In choosing what to do about the back of the pilot to attach it to the swivel screw head, I think that if needed, you could use a Zona saw to get into the main top part of the metal and make a shorter radius attaching tab. I think you could also make a lot of the work easier by taking the cross member out of the shell. (Duh!) Another way to get more clearance in this area is to use a Dremel grinder to take the top ends from the motor frame where they protrude at the front, being careful of course not to get metal shavings into the motor. (Pardon me for noting things that you experts take as a matter of course.) And of course, any place you think metal to metal contact might cause a short, you can dab on the liquid electrical tape. You can also grind away the angled area at the front of the cross frame where the ends of the drive rods go on the 1688 for still more clearance.
One last question...This makes three, I think. What engine can be a donor for a cast trailing truck? If all this is successful, I'll post again with pictures.
I am a moderator on another Forum and am very impressed by the scope of this site. Well done!