one just sold on ebay
http://www.ebay.co.uk/itm/110755255210
http://www.ebay.co.uk/itm/side-winder-sidecar-/260736315507?pt=UK_Motorcycles&hash=item3cb5187073#ht_500wt_1156
go on neuman I know you want one!
saw that OT, wasn't very enlightening, anyway the law was 16th december 1971 16 yr ols had to have pedals to ride a 49cc motorbike. ie it became a moped
all the valves need to do is seal. look for broken valve springs as that helps seal them too. I'd decoke and lapp in the valves, which you need a valve extractor clamp ( or make one from a G clamp,google it)
never had gaskets go on me, i even make my own.
The most important one is the head gasket, sealing in the expansion gasses!
you need a torque wrench too, impossible/dangerous to guess tightening forces
tappets? pushrod stuff OG
looks like the head needs a decoke, and poss the piston rings are not sealing properly.
what you should have done is taken a video before you stripped!
you now need to check with your manual how much play is allowed and if the bottom end can be moved up and down at all (that may indicate the knocking sound you can hear)
that's all I can profer up to now!