Hi Kent! Sweet is correct on your block. I too have a 261 with a "5913" head. It was originally on a 235 but will work just fine on your 261 unless you want to soup it up a bit with higher compression. Then you want an "848" head but really isn't necessary. The 261 has plenty of torque and power with the 235 head.
You should have ports for a full flow oil filter and there is plenty of data for that on this website by using the search menu. As well as Sweet's site, I have pics of the rebuild of my 261 on the site link below including the installation of a full flow remote oil filter.
The oil line you refer to is a modification that was done many times to bring oil up to the rocker arm assembly. Under your pushrod tube side plate, there should be an oil line (1/8" or so) that runs from the cam bearings up to a spot near the head. Sometimes this line would get clogged with crap and instead of taking the side cover off and cleaning it, a mechanic would run a line from the oil gauge port on the left side of the engine around to the right side of the engine and hook that up to a drip tube to lubricate the rocker arm assembly. Again, lots of info by using the search function.
Finally, is your tranny a three on the tree?
