Okay, I know this is not going to help the OP, but it's worth mentioning. You do not have to remove the side cover to see if you have hydraulic lifters or solids. You can take the rocker assembly off the head, then remove a rod and shine a flashlight down in the hole. Easier and doesn't require a new gasket.
If you have hydraulics, there are retaining springs on top. They look like little retainer clips holding the assembly together. The solids just have a machined area for the rod to sit on.
I was doing some maintenance on my 261 and since it's been awhile, I wanted to verify. Sure enough, that's the easiest way if you were forgetful and forgot to write that small item down somewhere.
