Once cast, the walls "just" needed to be bedded into cement alongside the line. Our track is laid on a bed of breeze blocks so there is enough spare either side of the track to cement too for much of the way, and where there isn't, the ground is compacted enough to allow for foundations.
Keeping the walls far enough away from the rails to avoid being clouted by Ragleth cylinders was achieved with a simple piece of wood Blu-Tacked to a Playmobil wagon. There were two, but one fell off.
Not only did the wagon help with gauging, it could have plastic tubs of cement placed on them and then shoved to my dad who was fitting the walls whilst I mixed muck. Around the back of our oval, it's a bit tight between plants and this turned out to be the easiest way to deliver materials.
This work wasn't fun, but hopefully, combined with the rail clamps, the line in this difficult to get at spot won't need much attention once the ballast goes in. Come spring, the plants will soften the edges a bit and it will look nice and tidy.