Do big-end bearings need running in? I've just replaced mine, should I nurse the car for a few hundred miles or just get on with it? I don't see why they would need it, after all they shouldn't be in contact with the crank, but better safe than sorry?

As long as they are getting oil they are the best they will ever be, so, no just run them as usual. IMHO Ray

big ends don't actually make contact with the shells due to the oil layer so running in shouldn't be necessary. just make sure there is oil pressure before starting up.

Oil pressure is good, solid 40 psi at 2k rpm and 10 at hot idle (normal numbers for this engine I think). Cooler is keeping oil bang on the middle of the gauge (about 90 something degrees). So the new bearings should be happy. I installed them with assembly lube and spun it without plugs in until the idiot light went out so first-start oil pressure was fine.

I spotted a momentary dip in pressure (about two seconds while idling) when it first got hot and the oil thermostat opened so the air in the hoses to the cooler came into play but not sure how you could avoid that, it's impossible to completely fill those?

I kind of agree, can't think of a reason they would need running in, except possibly if I've buggered something up and it lets go in the first few hundred miles, I'd rather it did it at running-in revs than at the redline. But obviously that's not going to happen, have to try and think positive with engine #3...