well they are both 20V engines... the silvertop was the original one, and easily the most common, and as a result, the cheapest... the blacktop is the newer one, only released in a few cars, and more expensive... the only real difference is the blacktop has VVT technology... you'll easily be able to pick up a 20V SX seca for under 2 grand, but it would be in questionable condition... it depends how much you wanna spend i guess... if you wanna get JUST the engine, check out the jap motor import places for a rough idea of prices... and as far as modifying a 16V over a 20V, the 16V IS easier because theyre more common, and they came out as the 4AGZE, so all the performance parts are there... the 20V was a fairly shortlived engine... its an awesome idea, but for my project, ive decided to opt for a 16V just cos parts are cheaper and more available...