The Piggott "Triumph TR" book is a good reference. He also has a book on the TR4/4A/5/250/6 but it is not as good a reference on running changes for the early TR6 production changes. Graham Robson also has a TR book, not so much text on running changes but a fair number of decent pictures.
Many years ago when George Raby was Chief Concours Judge for VTR, I had worked on a Concours Judging Guide for the TR6. Here are the quick and dirty engine compartment notes with rocker cover and fan shroud question up first. While some of this stuff in the guide notes was for all production, the emphasis is on the North American market cars.
On a 1969, the rocker cover is chromed, the painted one was 1970 up.
The fan shroud is forward of the radiator.
Single tube downpipe.
The crankcase breather valve is the diaphragm type, same as the TR250. 1967 and down MGB used a similar valve, the diaphragms are interchangable but the unit assembly is not. Crankcase breather set up and intake manifold changed for 1970.
Fan blade on most 1969 cars was the 8 blade, yellow plastic as used on the TR250. Some later ones used the seven blade yellow plastic fan found on the 1970, 1971 and 1972.
Washer bottle is oval, motor housing is square, square washer bottle began with 1971 cars.
Not obvious from the outside, but the crankshaft, flywheel, pilot bushing, are the same as the TR250. These changed in 1970 and as long as the components are in the correct sets, either the early or later crankshaft and bits can be used together, but not mixed.
Distributor is double vacuum (advance and retard) like the TR250 and many of the 1970 cars.
Looking at the picture you have attached, you have the correct 12 hole wheels, 5 1/2 x 15 with the stubs for mounting the ROSTYLE hubcaps. Don't knock those stubs off, if you are ever lucky enough to find a set of the ROSTYLE hubcaps, you'll need those stubs. Later wheels had 15 holes and no stubs since they used the small center caps like you have fitted.