Hi,
The Bonneville engine had what came to be known as a "splayed" head, meaning the inlet ports pointed outwards toward the sides of the engine at an angle similar to the exhaust ports, for the twin carbs.
The 6T (Thunderbird), T110, and other single carb 650's had a screw-on manifold (two screws vertically at each port) joining the PARALLEL ports in these heads to mount the single carb.
Conversions to twin carbs were popular which consisted of bolt-on pieces for mounting twin carbs onto the parallel-port heads.
So if your head casting has the ports spread with large diameter screw in extensions to facilitate twin carbs and does NOT have the inlets coming out parallel, with the ports faced off with two screwholes sited vertically above and below each port for the single carb manifold, then it is indeed a "Bonnie" head.
As for your valve clearances, if it does not make a very audible tappet rustle, (some might even call it a rattle, although I think that's a little unfair) then the clearances may indeed be too tight.
The clearances depend on the type of cams fitted - most of these engines only need .002 inch (.05mm) inlet and .004 inch (.1mm) exhaust, but for engines with "ramp" cams fitted (quietening ramps to take up clearance gradually, distinguished by a wheel like symbol complete with spokes before or after the engine number) these clearances should be increased by .008 inch (.2mm).
Whether or not your engine has this symbol, it is wise not to make assumptions over which type of camshaft is fitted, as it could have one or the other or even a combination of the two.
The only way to know for sure is to fiddle about with the feeler guages and rotate the engine so that when the inlet valve for one cylinder is at full lift the clearance in the other inlet is checked and the feeler or thckness guage is left in place and the engine turned over until the tappet closes tightly on the guage. If this happens just before the valve visibly starts to open, then that cam is not a "ramp" cam. If the feeler is gripped tight with still some way to go before the valve lifts, then it is a "ramp"cam.
Check one of the inlets and one of the exhausts, the inlets should match each other as should the exhausts as the Triumph twins have two camshafts, one for the inlets and one for the exhausts.
If your camshafts are a mismatch, don't let it worry you too mutch, as it will run ok provided the clearances are set to match the cams fitted.
Mismatched cams is something I have always regarded as a "bodge", and not best practice or something I would do, but I have come across it a few times.
I hope this is useful to you, and wish you luck.
A.
