@trclac - looks like a very straight forward install. What is the distance between the 90 degree elbow and the blue colored device on the outlet side?
For DIY, I’d probably recommend the underground parts (will cost a little more and I had to order the parts in as they weren’t in-stock locally), as things come apart at the green fittings:
I’d go bottom up on the installation. Turn off the water. Take off the insulation. Measure 2" up from the blue device and make a cut using a hacksaw or the folding Jab saw with a fine tooth blade. Measure up 15" from this cut and make a second cut. I used the Orbit PVC-Lock bevel tool that came with the release kit to clean the ends. Push on the Orbit PVC-Lock and Orbit Manifold male piece on each end. Assemble the Orbit Manifold swivels, PVC-Locks and Flow meter, slide into the gap and close the manifold threads. The end PVC-Lock devices would be either 1" on both sides or 1" to 3/4" reducing if the system is 3/4" PVC.
A professional installer might just rebuild the section of PVC on the outlet side, but the other option is to put a cut midway between the backflow device and the 90 degree elbow and then get a coupler to put that piece back together again after installing the flow meter (using the cut to provide movement to install the PVC-Lock fittings and then there should be enough left/right flex in the vertical pipe to push the two sections together. This option would use 3 - couplers, one on each end of the Flow Meter and then one between the backflow device and the elbow (this one could be glued or PVC Lock for DIY).
There is no reason a plumber or irrigation installer should flinch at the “plumbing” work on this.
There is no gluing involved, so if one can measure (twice) and create a fairly square cut in the PVC pipe I think it is within DIY capability. I’ve probably confused you with all the options. Either way, easy. Don’t forget to reinsulate the pipe.