You won't need that much primer if you're only doing the engine bay right now. And if the engine bay is in good shape(not needing any bodywork, not all scraped up) you don't really need the 2k primer. A quart of SPI epoxy and a quart of activator is less than a $100. You could spray a couple of coats of epoxy and go straight to topcoat with no sanding. With two sprayable quarts, you will probably have a bunch left over. Unlike some other epoxies, the SPI stuff sands pretty well, so if there are any issues you could sand them out. On my duster's engine bay I used Cromabase f6 basecoat with SPI's epoxy, 2k primer and clear.
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