You don't have to remove any covers to do the primary chain adjustment. Just unscrew the big flat (slotted) filler plug about halfway along, towards the top of the chaincase.
The adjuster nut (or drawbolt ) is the one on the bracket with the U-shaped cutout.
The bottom pivot is the big extended hex head right underneath the gearbox kick-start cover (ie on the off-side) . It's probably the only hex in that area that isn't a nut on a stud (most every other fixing in that area on the off-side is a nut on a stud). Be aware that this a special bolt that extends right across and carries the 5/16 nut (on its reduced diameter, extended tip) that secures the bottom of the primary chaincase, underneath the clutch cover. You need to slacken that nut before slackening the lower pivot bolt (and then re-tighten it as a last thing when you've finished).
The top clamp should be a long stud, going through just the engine plates and the upper gearbox mounting. It's not the one that goes through the frame lug. The nut to loosen is below the oil tank - the stud is held captive in the engine plates so you don't need to anything with the nut on the other end, behind the primary chaincase. As I remember it doesn't really matter if you undo both these nuts - as long as you do them both up afterwards.
Two things to bear in mind:
- as other have said, moving the gearbox to adjust the primary chain also changes the tension of the secondary chain, tightening the primary chain slackens the secondary. (Loosening tightens the secondary and to deal with that you need to slacken the secondary off first - obvious, sorry.)
- final tightening of the gearbox clamp and/or pivot bolts can (in my experience it invariably does) alter the chain tension, you need to check carefully that after the clamp and pivot bolts are tightened up the chain tension is still correct (this bit can be quite exasperating - it's why Nev says not to slacken the clamp and pivot bolts off too much but if you're not used to this it may not be easy to work out how much is too much and anyway final tightening up can still mess up your settings.
Chain tension is 3/8" total slack, through the filler-hole in the chaincase. That's measured without putting any great force on the chain to really push it to its extremes.
( 3/8" is at the loosest spot - again, obviously! I usually find that by sticking a finger under the chain and slowly turning the engine over with the kick start, with the spark plugs out on a twin, to get a feel for where the chain is floppiest.)
Hope that ain't too many words.
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)