firstly get the engine on a stand and make a pointer this will attach to a bolt hole and must be sturdy so it doen't move as you carry out rest of operation,you will need a dial gauge a set of vernier sprockets a timing disc and alot of patience and concentration use a dial gauge to determine when piston one is at tdc you do this by making a note of when the dial moves in either direction from the piston being at top of stroke the tdc is the middle of these pointswhen the engine is at this point place disc on so that the pointer is at zero on disc then place head on making sure not to move the pointer or the head will have to come off again. you now need to determine the positioning of the cam you will need dial gauge again to do this i can't remember wether the first valve needs to be fully open or fully shut but one of these youdo this roughly and move the crank to the given figure in cam data but opposite as this data is based on the disc being mounted on back of engine ie if instructions say clockwise you move anti clockwise to that amount. you then place your vernier sprocket set as near as poss to this position. then you need to use the adjustment on the vernier to get it perfect. to get it nob on you use dial gauge on valve one and when it's at is's most open or most shut can't remember which you take readins of when the dial moves either way. the middle between these two figures on the disc is the correct figure tighten everything up and should be sound check it through several times as it's very easy to make a mistake especially as you are working in reverse. i understand that this may not be clear as explaining things is not my strong point and it's a while since i have done it but i hope this helps you. another option if you have means is to make a plate to mount engine on it's side so you can work from back.