Ok say i have a block that originally came with regular hydraulic lifters and flat tappet cam. Could i put in a hydraulic roller and hydraulic roller lifters as a direct swap with no machining?

 

Yes and no.

A factory roller block has 3 tapped bosses in the lifter valley in which a "spider" is bolted down to. This "spider" presses down on 8 dogbone lifter retainers. These lifter retainers hold the tappets square to the cam. Also, up front, there are 2 holes drilled and tapped for the cam retainer plate. This plate prevents roller cam walk. This whole overly-complex system composes a factory roller setup. So if this is the "hydraulic roller" you speak of, then no, it can't be dropped right in as these bosses and the front 2 holes are needed. Also, theres a bit of clearance issues on the sides of the lifter valley, but that's no biggie.

However, there is also a retro-fit roller setup that is far more simple and original in design than this bastardized GM factory roller. This retro-roller just uses simple link bar designs to hold the lifters square, no central spider or dogbones are required. These can drop right into a flat tappet block.

 

True, to do the conversion however, is not inexpensive. You may want to consider going with the stock type cam and just do the roller rockers and a good roller timing chain if you're low- buckin' it.