Well, since the thread was revived, I thought I'd post on this subject.
In the Silvia forum, there is an Australian member who swapped a VH41DE(2nd gen Q45) into his car. The VK's dimensions are probably similar to the VH's, so the swap can probably be done. It's an old post, so reading it will probably require a search.
As for the issue of engine weight, a VH45DE weighs only 521lbs, according to an article I saw in Road and Track. The VK is probably similar. The weight really isn't much when you think about it, comsidering SCC said a KA was 493lbs. So sure, the car gains about 30lbs, but don't you think that could be saved elsewhere?
Even if you don't go for a weight reduction, think of the power gains. With a stock VH41DE, the weakest of the Infiniti V8s(266hp stock), you'll have over 100 more horsepower than with a stock KA. With a VK, the gains go up to nearly 200hp. Keep in mind those motors are stock, so you wouldn't have any compromises on reliability.
Btw, if you want to go with a domestic V8, the LS1 only weighs 411lbs or so. Not only is it aluminum, but the OHV hardware also makes the engine lighter(vs OHC), with a lower center of gravity.