From what I understand - the lifter bores in your older block are not deep enough to accomodate the OE roller lifters. I have heard of two work arounds for this. 1 - a small-base-circle cam, which allows the lifters to stay lower in the bores but requires custom pushrods. 2 - I think some aftermarket roller lifters (the ones connected by bars) might fit - check with crane cams.
no point in roller lifters without a roller cam. In fact, it may be incompatible since hyd lifters are designed to rotate in their bores as they work and a roller lifter, obviously, cannot do that...plus, hyd cam = iron, roller cam = steel.
But yes, the non-roller block bores are not deep enough without the modifications mentioned above.
Of course, roller lifter with roller cam. Small base circle cams are a "work around", but not anything near an optimal solution. There are a very few lobe profiles available and the cam cores are weaker due to reduced base circle. If you are building a cruiser with a mild cam and do not plan to see hi revs, okay. Otherwise, a much better solution is to use the Crane link-bar lifters with a standard roller cam. This is all addressed to a hydraulic roller. Solid roller cams/lifters do not have any issues regardless of new/old roller/non-roller block.
Anyway you go with a roller cam in a non roller block it'll set you back at least $600 for the whole works. Just isn't cost effective compared to starting with a roller ready block.