4-cylinder: The earliest arrangement - pointers below, but only at TDC, and 5 and 10 degrees before (Haynes).
Haynes calls this 'later arrangement' but it still has the pointers below, but additionally at 15 and 20 degrees BTDC (Haynes). This is the only arrangement that my workshop manual shows.
This on a 1970 18GH from Bill Etter has five, of varying height, but with the first one seeming to be the longest instead of the last. From the Parts Catalogue 18GJ would be the same, although by this time non-North American 18GG and GK engines had the timing marks on top:
Peter Basher writing on the MGOC MGB Technical forum shows this version on his 1970 which appears to have four pointers. Going by Bill Etter's it could be that the first pointer (closest to the cover bolt) has been snapped off, possibly because being large it was confusing as to which was TDC! Engine number not known but from October 68 non-North American engines should have had the pointers on top:
The later arrangement - probably on all 18V engines - above and angled towards the alternator: (Leyland Workshop Manual)
V8: Pulley markings up to 10 degrees, at 2 degree intervals, for both BTDC and ATDC
The single pointer is adjustable, which on the face of it is simply to cater for different pulley sizes ... but!
You can clearly see that when looking directly down on the pulley markings, there is a difference of about five degrees between fully out and fully in, which would have a significant effect on timing. My pointer was set fully in i.e. close to the pulley, but I'll have to check what that represents as far as true TDC goes.
Although I bought a modified timing pointer from Rimmers I can't find any way of mounting it to the new front cover, so have to fabricate my own. With the old engine, front cover and water pump at home, I decide to best place to mount one is on two of the lower water pump bolts - one that goes right through the front cover and the other just into it. With the original pointer (which I had lost, but found again when it came back with various bits from the engine man this week) I was able to make a card template, and from that cut one out of sheet metal. With the pulley (which I now have back as well) in the front cover I turn that so the original pointer is over the TDC mark then remove that and fit the new one, for final tweaking of bolt holes and pointer angle to be in the same position. As the water pump and crank are in the same positions relative to each other on both old and new covers, the new pointer does the job.
Checking timing marks and adjusting the V8 pointer: Knock the ceramic insulator out of an old plug and insert a length of dowel. I was considering fixing the dowel in position, but opted to leave it sliding (but not loose) and marking it instead.