The B28E is the european version of the engine that went into the D for sale in the US (the B28F). The B28E is found predominantly in (European) Volvo 760s up till 1985 when they went to a B280E which you can read about here:
viewtopic.php?f=12&t=1521I think Eagle Premieres in the states have a B280F engine which some people put into their Ds.
But back to the original question - the basic difference between the B28F and B28E engines is power. Out of the factory B28F = 130bhp, B28E = 156bhp. This is for two main reasons - a restrictive catalytic converter and lower compression on the B28F. Most people over here get rid of the cat, but the lower compression you can't do anything about (well, sensibly anyway!).
Problem is there aren't many B28Es kicking about any more, and certainly not very many with low miles as those big old Volvos have been racking up motorway miles for the last 25 years, so I was quite lucky to find one with low mileage.
There are some who disagree with swapping out the stock engine (see my earlier thread here:
viewtopic.php?f=13&t=1483) but the way I saw it, I'm really only returning the car to the spec it would have had if DMC had remained solvent long enough to sell the car in this country...