I would be surprised if they did pay up, scrap yards only usually give a small warranty if your lucky.

if the secondhand engine was in good condition Why did they need to s/f new gasket? this engine is prone to h/g failure and scrap yards were full of these cars years ago for that reason

I would suggest if you like that motor, as a mate of mine does, try and get the diesel, its far more reliable and is bullet proof,

imo, you are going to find it very difficult to find a good petrol unit

I remember having much the same happen to me 30 years ago (not this particular engine, of course).

I even hired a van to take the engine back, but when I got to the address there was no sign of the supplier.

In the end, I bought a rough but running model of the car, and swapped the engine over - it came with a couple of weeks of MOT, so I was able to test the replacement engine properly.

I am afraid the 1800 engine is notorious for head gasket failure and subsequent warping. The engine was designed to have a low water capacity to speed the warming up process (saves a thimble of fuel!). A version of this engine was also fitted to the MG TF that had similar problems - I believe owners of these have since made cooling system modifications to improve the water capacity of the system and improve reliability

When repairing the head gasket you need to ensure the engine is not damaged/warped otherwise it will fail again. You also have to bleed the cooling system very carefully to avoid having ANY air in the system - this is improtant otherwise you will cause the failure of a perfectly good engine

When you do manage to get the engine running reliably change the coolant every 2 years being careful to bleed air out of the system. One tequnique is to set up a temporary large water container into the system (small hose from header tank attached to a pipe fed from a tap on a camping water container) and slowly drain and fill the system at the same time flushing through new coolant. This uses more coolant so is more expensive but does not introduce air into the system if done correctly

The Rover 75 was a great car but not with the 1800. Most 1800 versions of it are no longer running but you see pleanty of the great diesel (BMW engine) and V6 petrol still on the road