It would clean up the front end a bit, but you would lose some of the infinite adjustability. You could use one size smaller square tubing that could slide into the boom tube.
Cut a keyed slot in the bottom and weld on a couple of pieces of small tubing on one side and some nuts on the other to clamp it down.
Or, you could drill a series of say 1/4 inch holes every 2 inches or so for a span of about 10 inches at the end of the fixed boom and double pin the extendable boom into position.
I built a stinger boom lift for a forklift at a boatyard once that worked just like that. Although it was used for lifting up and down, not fore and aft.
To get a nice interference fit between the tubes, I'm thinking you would need to maybe sleeve the fixed boom tube with some UHMW plastic, or weld some very thin plate on the extendable portion and finesse it with a flap disc to get it to fit and slide properly.
Maybe a coat of some very thick paint on the sliding portion, for interference and abrasion. Like a bedliner material, or an epoxy paint.
Most of the factory tadpole trikes do this with the aluminum tubing of their booms.
Does that make any sense? Maybe I need to dig up some visual aids.
Anybody have any other thoughts or ideas or maybe some definitive yays or nays? Maybe its just too much extra work, for something that already works just peachy?
Got the steering booms on this morning. Had a lot of confusion here and there. but once I cut the angles I only had to fine tune it once to get it to fit right.
On another front I laced my own rim the other day too!
Didn't have the right spokes, just used the old ones (which were too long) but they worked fine for a practice run. A soon as I get the correct length I'll be able to lace them up no sweat. Sheldon Brown has all the answers. :-)
So far the build has gone pretty smooth.
Although, I think my main boom ended up a titch too high somehow. Not quite eleven anymore. But the wheels are 90 degrees and seem to work ok. Guess we'll see if that effects anything down the road.
OK, onto the next step!