1. That return line routing was a common re-routing that was only needed/used if the internal oil-feed was providing inadequate lubrication to the rocker arm assembly. After-market oil-flow diversion kits (I think non-GM - 6 Cylinder Rocker Arm Lubricating Kit) were sold for this purpose. Usually people/mechanics just bought an adapter/Tee, an oil line/tube, and necessary fittings. Some people think that this is a "cob-job", but it seems to work OK, at least for a while.
2. Unless you engine has be converted for using a full-flow oil filter, a by-pass filter is required (if you want a filter). If your oil-inlet line to the filter is a small diameter (maybe 1/8" inner diameter) it will work as a by-pass filter (about 10% of the oil flow goes through the filter - the rest of the oil flow is directed to oil journals in the block. This by-pass filtration works fine.
