Rear chain tension - plunger frame

I am doing the chain adjustment on my 99 today , I find the best way is to leave the bike on side stand  and lay over the rear of the bike and reach down to feel for slack. The bike is lightly  tied down on the ramp with a ratchet strap each side  so it can't missbehave .I am having a tussle as the frame is twisted and I am having to compromise between wheels in line or sprockets in line .

As far as I know there should be no difference in chain tension in any position of the plunger suspension because it moves in a straight line unlike swinging arm which moves in an arc so adjust it on the stand to give the correct tension With swinging arm I check it by having the bike on its wheels with me sitting on it and moving it forward and checking the tension in different positions this is to allow for chain wear

HI Ian, It sounds like my method  (with the weight on the bike) should work. However  With your  design  I would also check there is a small amount of slack with the bike on  center stand (unloaded) and again with the suspension fully compressed using a good ratchet strap accross the bike . Once established that both situations give the same result (hopefully!) then the unloaded  on the stand method is an easy and very convenient  way to keep tabs on it.   I have been adjusting my chain  using a vernier caliper  on both adjusters to get the sprockets in line as the chain run cant be seen on my bike  and a bent frame at the front  means if I line the wheels up the chain tension goes all over the place !  A small missalignment of the sprockets plays havoc with the adjustments.  Its a Motoliner job. 

Norton's own handbook for 1947/48 says that for sprung framed models;

"track up the wheel and adjust until there is 3/8 - 1/2" up and down movement midway between the sprockets

NOTE.- It is important that this condition is obtained with the weight of the machine on the rear wheel"

and then I ask the good lady to hold the bike up as I check the slack. Job done