The parallel port head is only parallel on the outside, once inside you have the angled ports of the TR7 aiming the intake charge at the spark plugs. The TR7 head in turn is just a TR6 head with a modified casting for the 10th bolt hole, added material to the outside of the inlet entry ports to allow room for machining and threading for the steel carb stubs, (which are parallel) and a chamfered combustion chamber lip to match the larger bore of the 750.

The new TR7 head castings as seen on line appears to be the parallel inlet port head casting with the extra intake material still there but machined for the single carb manifold...might be a good head to have for some custom dual carb mods or a... straightened out port … single carb head for better flow than short stock single carb manifold. I wouldn't mind having one with the KB valves and guides and springs but just wonder about the quality of the valve/guide job? Just thinking about things.

Back to the original would be fairly easy to weld in a couple of flush aluminum plugs to replace the steel threaded in stubs, line up a stock TR6/7 inlet manifold, drill and tap for the manifold studs or use the stock steel stubs and do as Dmadigan suggested. Nothing at all wrong with a torquey, responsive TR6/7 around town which will usually outpull 99% of the ill tuned Bonnies you're likely to come up against.