I'm far from local but the way I do it on mine is to assemble the centre and backbox and hang them on their hangers as far back as I can get them.
Then I lay under the car so my feet face towards the rear bumper and head under the subframe, then locate the cat on the manifold and have the two nuts just on the bolts so there is a reasonable amount of movement there, then push the centre section back whilst locating the cat into the centre section, once that's in place I tighten the nuts up a bit then pull the centre section and back box forwards until they are in position and clamp them together.
It's a fiddly pain in the arse but can be done on your own with a bit of patience.
I've done it a few times now on my own, I think it helps to use the flexi ratchet type spanners Goethe manifold-cat bolts as they can be a bit tricky to get to when doing it on axle stands.

________________________________________

Goldie the track car.

Thanks for the advice!

I've got the centre and back box hung (bar a bit of fine adjusting once it's all in place) but where I am struggling is with the decat / manifold getting springs, washers and nuts on... I think I'll try getting the car higher on stands and do it as try as above! I'll give it a couple of days as its doing my head in!

Thanks,
Craig