The tube in the pass-side gallery will allow only the use of a solid or solid-roller cam, as it cuts off supply to lifters.The cross over tube diverts oil and either camshaft type may be used.
After high speed bearing failure I have tubed a block and also added a plug(behind the camshaft thrust plate and plugged the gallery over the number 1 main intersect feed.I run fully grooved main bearings and have great oil pressure(hot and cold).
I would recommend this proceedure for anyone using a solid cam in a LA block who has encountered previous oiling problems.The tube mod provides effective oiling to the mains as opposed to factory layout which can struggle under high velocity conditions(the oil can't make the sharp right angle turns,usually into number 2 or 3)