I shortened mine long ago.
I simply figured out how much I needed to shorten it, cut that much out of the tube, and used a plumbing aisle PVC coupling (maybe CPVC?) to splice it back together. I used proseal to seal the thing and 3 internally wrenching set screws on each end as a secondary holding mechanism. (The proseal and screws came after the first time I assembled it and the PVC glue joints failed).
Then I painted it Lycoming grey.
For the dipstick, you can drive out the roll pin, pull the rod from the cap, and then drill a new hole for the roll pin at the appropriate distance from the first hole and reassemble with a new roll pin after shortening the upper end of the rod.
On mine, I didn't shorten it, I just used a pipe cutter to cut new marks for oil levels. I calibrated those marks one quart at a time as I filled the crankcase.
Hope this helps.
