Most ringed Schneurle engines have pinned rings because the ports are so large although I just had a look at my OS 40SR which uses an unpinned Dykes ring but the exhaust port has a bridge in the centre. All the earlier cross flow engines had bridged ports so they didn't need pins either. In some ways this is a better system because then the ring can rotate and wear perfectly round.

Rings should always be removed and fitted in a spiral because this gives the least amount of flex and strain (especially important with a Dykes ring). Lift one end out just far enough so it can rest on the piston crown then very slowly work it around out of the groove. As it comes out the free end will slowly move across the crown. Installation is the reverse by twisting the new ring slightly until one end will just fit in the groove then work the rest in carefully.

If I remember correctly the proper end gap is about .0015" to .002" per inch of bore diameter.

And while we're on the subject, does anyone have Frank Bowman's details? I lost them in a recent hard disc crash