(Hopefully not IBTL, and I'm not starting a flame war) (Just proving that I'm insane)
Pushrods are guzzlers, you say?
I'll compare the archaic 235 cubic inch Hi-Thrift Chevy 6 with the 2JZ-GE. Both are (relatively) similar in size, they both are straight sixes. The funny thing is, they both get the same fuel economy. 18-21, regardless. Here's where you might say, "DOHC, duh!" but, the 235 is bulletproof. It was designed in 1927, and stayed virtually unchanged until 1963, I believe. In a 1960 Chevrolet Biscayne, (a car that weighs over 3,575 lbs) a lone Rochester monojet (one barrel) breathing through a restricted HOT intake and out of a restrictive exhaust manifold put out 135 bhp @ 4000rpm, and 217 lbs. ft of torque at 2000 rpm. Now, If I had kept the "stovebolt" in my chevy, I would have been able to expect 19-21 mpg all around. It's thrifty, but not that thrifty because it has to struggle with all that weight. It would actually get even better mileage and power with a simple set of headers and a 2 x 1 intake. (even more with a holley 390cfm 4 barrel, with a few DCOES, a stovebolt can slay many smallblocks)
Consider this, now.
My deceased lexus got no worse than 17, and no better than 22 mpg. The 2JZ-GE put out 220 bhp@6,000 rpm and 210 ft.lb of torque @4800 rpm. That's in a 3,498 lb. car. Now, you still probably think that pushrods are crap, and that the mighty DOHC is still more efficient. Let me ask you a question. What does RPM mean? Revolutions per minute. How fast the engine is turning to put out a certain figure.
Which is burning more gas at it's torque figure, the choked up stovebolt, putting out 217 @ 2,000, or the 2JZ-GE, putting out 210 @ 4,800?
If pushrods are so awesomely bad, how the hell does a design that's 79 years old get the same, if not better gas mileage than the DOHC toyota?
(Don't get me started on the reliability..

)
Again, why not a Datsun 620?