Tony,
Although there are detail differences between your rocker gear and the DT type, I would think the general set up is similar. The through bolts have hardened steel sleeves that the rockers pivot on, so the bolts may be just stuck in the sleeves! I would suggest locking 2 nuts together on the top of the bolts to see if you can start the bolts turning. If they start turning reasonably freely, but won't come out - they are almost certainly in plain holes in the rocker pillars, but stuck in the steel sleeves. If the bolts only move less than a quarter of a turn before tightening up again, then they are probably threaded into the pillars (and again stuck in the sleeves). If they are threaded into the pillars, you will have to be careful until you establish whether it is the top or bottom pillar that is threaded. If it is the top pillar then unscrewing the bolt will just jack it out of the sleeve - if it is the bottom pillar, then you will have to be careful not to spread the pillars (a nut and spacer against the top pillar will counteract the drag in the sleeve). If you are lucky and the bolt turns fairly freely to start with, a longer spacer and nut on the top should draw the bolt out (the spacer and rocker sleeve will just have the top pillar sandwiched, and not putting any stress on the pillars).
Hope some of this helps,
Regards and best wishes for the coming year,
Eddie.