The parallel port head was a move that Triumph SHOULD have made many years prior. Tuners in the fifties and sixties spend a lot of time and money correcting the inlet port shapes to get power and efficiency from this motor. Triumph apparently never looked at their results.
Re-angling the inlet ports was one of the things they did to help correct the tendency for these motors to detonate or experience pre-igntion.
What you have with the parallel inlet head is the final product of Triumph finally bending to winds of change and now you want to mess that up.
This just isn't how the parallel port heads came about! The only reason for them was to be able to easily use the AMAL
MkII carbs, which would enable Bonnevilles to keep on being saleable in the USA. It was an easy fix because the Tiger head was easily adaptable for the parallel inlet stubs, which hold the carbs nice and close and able to be supported by the airox directly behind them. If it had been feasible to carry on using the V head with MKII carbs, Triumph would have done it.
There is nothing remotely special about the E heads. The fact that they happen to work OK is testament to the overall brilliance of the engine design, rather than to any clever engineering of the inlet ports. A lot of racers go for the V head due to better results at top end.
If you want tractability, consistent smooth running, low maintenance and no noticeable loss in performance unless you're racing, a single carb head is a sensible move. I agree that twin carbs are better, if you want every ounce of horsepower at full throttle, but few riders of old Triumphs care enough about that to even notice.