There is, but it is a KV6 and if you wanted one of them yould get the 2.5L
There is a 4 cylinder 2 litre K series called the K2000 but it is a race/endurance race spec engine and consequently a bit pricey.
I read on the rover boards about the r65 but couldn't find anything about the weight sorry. I did find though that it is a standard gearbox as used in the BMW MINI and some Peugeot (and for rallying) so maybe it is strong!
I am not getting into the HGF debate, my belief is that it will happen to me at some point, but as long as I spot it early enough through checking coolant and oil every day then the bill should not be to large. Also with the new parts that the likelyhood of it happening again is slim!