The cam sprocket you need is a two-hole 28T. It is a CRF50/70 style. You will also want to get the CRF50 style cam sprocket bolts (the ones with 8mm hex heads) and the matching cam cover with the little stopper arm on it. If you use the original screws with the 9mm hex heads, they will contact the center of the cam cover and may break loose, causing the cam sprocket to fall off (ask me how I know.) If you use the original cam cover without the stopper arm, the cover can spin and fall off.
Thanks for the good advices!
I have a round cover that I believe is not original, it does have a thick tang inside, now I know why!
I bought two M5x12 and two M5x16 class 12.9 allen bolts this morning from the local hardware store, I didn`t measure the OD of the head but I will surely look into this, thank you!
I found a 21T kick starter spindle assembly on ebay, with a 37.72 mm OD gear, so I bought it, the guy measured for me, it looks like a match. Mine is currently 22T about 45mm OD, I haven`t used a caliper on it. so that`s 4mm less on the radius, that looks good to me on paper.