Hi Steve , yeah if your neighbours boiler is a kingfisher it will be a fair age , they were made by a company called potterton, they only have a few parts which make them pretty reliable , two stats , a gas valve , thermocouple , burners and a cast iron heat exchanger , not full of electronics like today's boilers , so not much to go wrong , but not very efficient by today's standards . The Ideal equivalent to the kingfisher was a model called 'mexico' , with similar setup . If it's a back boiler then it will probably be a Baxi . A back boiler is situated within a fireplace as opposed to a freestanding unit like a kingfisher .
Most of the boilers these days are full of composite plastics , some don't even have nuts on the fittings but are held in place with a O ring and circlips . To be fair I wouldn't say I've ever really had any problems with the plastic parts breaking or cracking in any of the boilers mentioned .
The heat exchangers on the new boilers are all either stainless steel or cast aluminium . I prefer the s/s as I find the condensate trap on the aluminium heat exchangers always fills with an aluminium paste caused by the condensate 'eating' the aluminium , it is a dilute sulphuric acid after all !! so make sure this gets plumbed to a drain and lime treated before it with a condensafe . Condensate eats / disolves concrete and copper over time so drains must be run in plastic .
With a house of that size I'd always recommend a cylinder , IMO combis are better suited to smaller properties that just don't have the space for a cylinder , there's also the advantage that should the boiler ever break down you will still have the immersion heater to heat the cylinder . The worst of combi's is having to throttle back the water flow at colder times of the year to get a decent rise in temperature due to the incoming main water being colder . This takes ages to fill a bath .
As an example in the summer the incoming may be around 15° , with a 40° degree rise @15lpm this gives 55° water at the tap . In the winter the incoming may only be 5° , which with the 40° rise only heats to 45° @15lpm , to get the extra heat into the water the flow rate has to be reduced so to achieve 55° you would need to run the tap slower , quite probably bellow 10lpm .
Should you decide on a combi I would also recommend looking at the existing piping of the hot water to the taps especially if you are on a water meter , I'd have the pipes resized to suit the combi and the runs to each tap made as short as possible , this saves having to run off loads of cold water before the hot reaches the tap . For most combi's it will recommend this in the instructions as the DHW pipes will probably be 15mm in and out of the combi , a lot of plumbers will connect the 15mm to the existing house which is normally 22mm , which creates the larger amount of water requiring being drawn off as above.
With a cylinder the water will be what ever you set the stats to normally around 60° - 65° regardless of the incoming temperature , the water will always heat to this and the flow rate at the tap will always be consistent . The plumbing to and from the cylinder will also be 22mm , so will be of correct size to any existing plumbing .
IMO you will notice the difference between the two with the cylinder being the better of the two .