If its the petrol engine (tb42 in heading td in description ?) then i did mine a few years ago. Actually fairly straight forward and as i recall the bolts are standard and I re torqued them after running a while.(used new bolts though)

The problem with mine turned out to be a kind of baffle that sits under the carb' that had somehow come loose and worked it's way thru' the engine - not good - so i left it out on repairing the damage and i didn't notice any difference in performance .So if you have the same - think about removing it !

Sold it later and got a TD 42 - head on this is Ok so can't really help-but imagine it would be comparable in difficulty .

My approach - if it helps at all - was to keep organised by using a packet of envelopes in a tray and keeping various components together and making notes and diagrams on the envelope itself .
I'm only a jack of all trades and it started first pop after putting it back together.

Cheers and hope you get more detail from others -PS if you are in sydney there's are a really helpful cylinder head shop in brookvale - opposite maccas and next to battery world - can' t remeber their name !