I have to refer back to my post where I wrongly assumed the models passenger0_0 had posted were Ariel cams and followers.
My explanation why a flat follower might be used for one cam and a radius for the other has indeed occurred with Ariels, and the reason is that subtle variations can be made this way, sometimes when using one cam lobe to fulfil both valve lift requirements.
I did an exercise some years back for members of the Ariel club, identifying and creating data files so that in future the club has data that will enable any of the cam forms to be re manufactured. During this exercise I was shown just how many different cam and follower combinations were possible, flat, radius, high lift. low lift, the permutations were considerable.
Time traveller,
you say the Picador profile has negative flank curvature, so this being the case you would not want to be rash and mate it with a flat follower, but there are many cam forms in other engines which have no negative component, yet are working with a radius follower. To use a flat follower as a replacement will automatically have the effect of increasing the area under the lift curve, while leaving the maximum valve lift and the duration unchanged.
Passenger0_0,
I have never seen an Indian side valve engines cam followers, but am much more familiar with Burt Munro's OHC conversion. Burt made his own cams using a jig he erected on his Myford lathe, from masters he made that were the inverse of the resultant profile. Sad to say, Burt's lathe which was used as a feature in the film, went missing after filming was completed, and as far as I know has still not been found.