I just can't see a dual plane big-port intake offering any kind of improvement on a low-compression 273... especially if you still have the stock rear hi-way gears, and an automatic with a stock convertor.
And here's why;
The factory 2bbl is good to at least 3200 rpm@100% VE (Volumetric Efficiency), more like 4000@70%; which with 2.76 gears is over 40 mph, in first gear. If your engine can only process 250 cfm then it doesn't care how many barrels are on it, it will still only process 250 cfm. If you need more than 250cfm, then you need to dig deeper into the engine.
Where did I pluck 250 cfm from?
a 273 engine means if you add up the swept area of all 8 cylinders, then you will get 273 cubic inches. But it only fires 4 cylinders every revolution which is 273/2= 136.5 cubic inches at one rpm. At 3200rpm it would be 3200x136.5=436,800, which divided by 12x12x12 to convert to cubic feet is 253 cfm....... if it could fill every cylinder 100% at 3200 rpm. But with the stock cam,pistons and exhaust system, that will never happen. 70% IMO is a generous number, so that would be 191 cfm. And I think your 2bbl is about 230 to 250cfm, which would be good to 4000 because the engine is rapidly losing efficiency.
The point is I hate to see you spend a couple of paychecks and come out little to no better.
But if you just gotta try it; I highly recommend to stay with a small-port design. And not just at the head but all the way to the plenum.
And I see you are in Colorado. If you are at altitude, the situation is even worse.