I have those in my Meteor... but you want the Metal Trunion version really. They are much better... for a fraction more cost.
And I have sprung oleos, which you pretty well need if you want it to last long term... especially on grass! I take off from a cricket pitch, but land on the oval's grass. And it is fine doing that.
Metal trunion version of that retract:
The oleos are a bit costly, but they are excellent and there isn't much else you could get to do the job as well anyway. I did use the stock wire legs/wheels, cut down to suit, for ages, so you can certainly do that to save money!
My installation is somewhere WAY back in this thread.
The main gear is SUPER simple.... but the nose gear takes a bit more time. Not too bad if you know what you are doing from experience, but if you don't have those clues etc it can be a big project!
The main notes are:
1) Nose: Make the leg fold FORWARDS
2) Mount the retract off its "top" - the side that is away from the trunion. Change the retract mount plate to the 'full' one. Just use one large plywood 3mm or 4mm plate put up into the cut-out nose area (part of the existing open area used too). Mount the steering servo into that same single plate (pre-do it all before epoxying the plate in!).
3) Use pushrod steering - I have an outline of doing that in my Blog (most people don't do it right, but if you do know how and why then they are the best system by far!)
4) Mains - just dremel out the existing plastic mounts to take the retract unit, that works fine and is strong... and dremel out some foam for the legs and wheels to recess into.