Hi, I am still interested if you still have it.
I just restored my '57 model 77. PIA to get parts, its a mish mash of left over model 7 parts & model 99 dommi parts, with a few 2 year only parts added in just for fun! The tank (if you can ever find one) will set you back $500-$600, then you will need the 2 chrome tank panels (different shape than the 88 & 99) figure $200-$300 a pair, then fix & rechrome , another $200, then 2 badges ( hurra, you can buy them new!) for around $70 a pair with screws, 2 ewarts petcocks with o-ring rebuild kits around $125 a pair, rear tank mounting bracket $100 (they come up on ebay about once a year), then body work & paint, maybe $400 or more. So a new petrol tank can be yours for the low low price of $1800!
The highest price I have seen a complete model 77 sell for was just under $5000, I probably have over $8000 invested in my restoration, not including any labor. Its one of those things you do for the love of the hobby, of as Jay Leno once said "if you make any money restoring antique cars & motorcycles, you probably didnt do it right".
Some of the other differences between the Nomad & the 77 are:
Nomad has a hotter cam
nomad has 2 carbs
nomad has a slightly different frame (lower engine cradle is tubular, not cast)
nomad has a slightly different seat
nomad has polished headlight ears, model 77 are painted
nomad oil tank is missing one of the tin pieces (on the back of the tank, facing the front of the bike)
different exhaust & mufflers
different shocks, front & rear fenders, different petrol tank, handlebars, brake & clutch lever (nomad had ball ends), no kickstart rubber on the nomad, rear frame loop bolted on the Nomad, no side stand on the nomad, separate intake stums with rubber tubes to carb on the nomad (2-1 manifold on the 77)
and yes, the swing arm on the nomad has an oval cross section for strength & to fit a wider tire. The nomad also used a different axle adjuster.
These are just a few differences, there are quite a few more!