<<Just finished with the trial installation of my Grove airfoil gear legs.>>
As it happens, so did I.
<<I used the parallel al angle method as described by Ironflight>>
Me too, worked fine. Don't forget to establish identical distance from a reference on each leg to the tailwheel pivot. Even safety wire is a little bit stretchy; I pulled mine with a fish scale to 4 lbs.
The Van's instructions have you tighten the inboard AN7, snug initially, and later torqued as some sort of clamp to hold things from moving while you drill the outboard 3/8" holes. Naaaaaa. In the first case, while doing all the preliminary lineup, cutting skin clearance etc, tightening the inboard AN7 may lift the leg up off the outboard wear plate. It needs to sit solidly on that plate to allow alignment in an accurate manner, so tighten the bolt just enough to get the slack out of things. As for tightening that AN7 as a clamp, there's a better way. Get the alignment spot on. Machine or buy a punch with a good 3/8" OD. Grind the tip with a well-centered low angle point (around 15 degrees or so), drop it in the hole, and whack it with your trusty 2lb shop hammer. Remove the hardware and you'll find a very good center punched mark to drill in steps, 3/32 then 3/16 then 3/8. You'll keep your alignment, no worries.
For those whose drill experience has not included big holes in 4130 steel, put aside the high speed air drill you use for aluminum. Buy or borrow a big slow speed electric drill with a 1/2 chuck, and get some new cobalt bits, not **** from the big box store. 4130 is easy to drill if it is in the normalized or annealed condition. That's not always the case after welding or machining, because 4130 is an air-hardening steel. If you heat it and then quench it (cool it quickly) it becomes very, very hard. So, if the fabricator didn't follow the rules and cooled the gear box weldment quickly, it will be hard to drill. More common is that the builder makes a mistake and tries to drill the weldment with a drill that turns too fast. Friction heats the 4130 under the tip of the bit. Stop drilling for just a second or two, and the surrounding cool metal instantly quenches the hot spot. When you start drilling again, you find that things have gotten very tough. You drill awhile, get tired and stop again...and uh-oh, repeat the process.
All of this is avoided (even if already quenched) by using new, sharp, hard bits and a very slow, powerful drill with lots of pressure. The weldments and wear blocks will drill like butter. Well, ok, maybe like aluminum <g>.