Even in Speedsters, because of the slight differences in inner body shape/construction with the different manufacturers, different details in each individual engine install and how the engine compartment is finished, seem to all be unique as to air requirements, how hot or cool they run and how they react to different ideas/ways to get more air into the engine compartment. With a Coupe it's a whole new ball game. I think what you're doing is a great idea and you'll have enough room, but mocking it up with some flexible tubing and mounting a tire will confirm, along with some experimentation and air pressure/temperature measurements and comparisons.
What I think some people don't realize is these bigger engines in their modified state actually radiate a lot of heat into the engine compartment itself (something that didn't happen with stock 1100, 1200 and even 1300 cc engines in their stock fully enclosed engine compartments), and there's a benefit to there being enough positive air pressure that not only do the fan and carbs get the air they require (very important for engine running cooling and life/longevity) but at least some of this radiated heat is removed via air moving through the engine compartment so it's not re-ingested (again, and again, and...).
Most of us run more powerful engines than the original VW engineers at Wolfsburg ever dreamed of, and even putting a dual carbed 1600 in an earlier Beetle without increasing air intake will cause 'issues'. I've seen and heard of lots of guys have problems with exactly this combination, and in every instance it was (at least partly) solved by getting getting more air to the engine. I've even heard of (read about, actually, on this wonderful inter web thingy) an engine lid collapsing on a Beetle during a 'rolling road' dynamometer run. If there ever was a case of not enough air into the engine compartment...
Engine compartment air pressure tests (with aquarium air tubing and a glass half filled with water) and air temp testing with a remote unit (the ideal being the temp inside the compartment being within a few degrees of the temp outside) will tell you when you've got it right. Alan's list is a good place for ideas. I do disagree with his last statement, only because if that's the only way to force enough air into the engine compartment, so be it. There really is no 1 right answer here.
Hope this helps. Al