Hi Ben. You seem to be misinformed about the RB series. Physically, they are more durable than the L series and cant stand alot more HP being put through them. Also Point 6 is completely wrong from an Australian point of view. We've had RB engines since 1987, so parts for RB engines are cheaper and easier to source than L series parts. Alfa: If you are after horsepower, forget the RB20DE or DET. Sure the turbo can make some power, but you have to increase the boost to get it, but you end up with a laggy engine - not alot of power down low and heaps at high revs. Aslo when you start messing with the boost too much, you have to modify the engine managment computer (piggy back units that modify the signals from the engine sensors), or go with an aftermarket computer, plus spent money on the dyno tuning it. The Rb25DET is a better engine and the extra capacity means it has to work less hard for the same HP that a 2.0 would. Rebuilding an engine will cost $$$ nomater what the engine is. Most of the money spend will be in labour costs. Turbo engines will cost more because of all the extra stuff you have to add to them. As for the L28, it has cubic inches going for it. Raise the compression a little, and have the head ported and polished, extractors. Use EFI for reliability and economy. I'd go for the L28, and spend the money you would have spent on fabricating engine mounts, intercoolers, and all the other costs involved (eg engineers inspections) , on the engine itself. It's period correct, wont require engineering to be legal. Wont be as economical as a 2.0 naturally asprited engine, but will be alot more fun. Another alternative would be the RB30E (VL commodore, Australian built R31 skyline). It may have to be engineered, but the 3 litre capacity and the fact that you can bolt one an RB25 twin cam head for improved breathing, and the availability of engines and parts (relatively cheaply) mean that its an engine to be considered. Builting an RB30DE would be easier and probablyt cheaper than building an L28 3.1 stroker. Or you could built an RB30DET, but i'm guessing that a bit out of your budget.