Now apologies for filling this with pictures and I wish you luck with this. You will curse and there is much cutting and filing to do. Look at the flash and pins on those wheels! The roof simply does not fit and there will be much sanding of the ambulance front face to do so.
OK first this is roughly where the parts will go;
Note next how the horses must be orientated due to their harness (I have offset slightly to clarify). Also I am trying to show how the draught pole and swingle trees come together. Note that the former is lying on its side and there is a curious triangular thing on what will be its upper surface
Those wheels and again you will see how the draught pole will eventually slide as a snug fit into the front axle assembly (once rotated of course)
Now this is probably where you struggled. There are four C springs, which, on the real thing suspended the carriage but here are decorative basically. There are four raised segments on the chassis members (arrowed) which show you where they should go. They butt up against them, once glued to the upper surface of the sub-frame;
Now here I have tried to show how it will come together. In practice I would not stick the springs on yet and I took them off again as soon as I photographed this. Also, the roof. Notice there is a "lip" on the undersurface nearest to you? That fits over the open door, so the roof must go on that way (if it fitted).
Now this is how the carriage really is secured. In theory there are two projections on the resin undersurface , one to glue to the rear axle, one to the back of the circle on the front axle. In practice neither reaches, but they are useful guides for placement and once more those four raised segments are where you will glue. Now I would attach the springs. The straps will need a slight trim and it is now obvious where Perrys intended them to go……..they wanted you to secure end to end to resin pins in each corner. I would just tuck them in as far more robust and glue.
Sliding doors at the side, open or closed as you wish. The Z is inside and the handles inferiorly. Rear doors are arched and the fit is obvious, open or closed. The ladder arrangement fits into, not on top of the very rear of the chassis. There are meant to be two slight hollows (you can just make out the far one) to accommodate the pivoting cross member. (raised or lowered and notice the angled base of the feet, so as not insert upside down)
and finally. Back to the draught pole. The chain is underneath and should be attached to the swingle tree. (Good luck with that). The two front horses pull through that. The weird triangle on top. Chop off the side nearest the carriage and bend the more solid bit as shown. Mine here is a bit oversize and not well angled but you'll get the idea. If you are wondering, that carried a chain to the two rear horses' collars to allow braking or even reversing.
The other message is how to attach the horses. I seem to have lost one swingle tree somewhere, but bend the single straight bit before securing to the horse (not as here!). Check carefully as mine are all different lengths and not all will fit all horses. Once well set, drop the curved bit down into the rings as shown. Mind you the horse I show here is a rear horse anyway!
Any further problems happy to help