which common block modifications do you do/know and consider worth doing? what do you think about the mods listed below?

Things I came across are:

.) chamfer bolt holes on deck
.) break/chamfer edge at the bottom of each cylinder
.) groove cam bearing holes to 12 o' clock (--> clock cam bearing oil hole to 12 o'clock for a better oil wedge)
.) drill hole in thrust main oil passage (from rear) to oil thrust bearing (also drill bearing)
.) bottom tap all bolt holes

Deburr and chamfer EVERYTHING

I agree.
If oil goes through it, radius and blend as well.

Which motor, block, are you working on?

69 440 block

I wouldn't due the oil mods your asking about to the cam bearings or main bearing thrust bearings
The cam bearings are fed oil from the bottom for a reason, all the pressure from the lifters is trying to force the cam sideways, not straight down, as it rotates so forcing oil into the bottom of those bearings helps the oil get spread up the cam journals as the cam rotates
As far as trying to help the main thrust bearing get more oil why do you want that?
BTW, I always use full groove main bearings on all my B, RB and 426 hemi builds to help oil the rods and cam bearings full time I like to use the full narrow groove truck main bearings also, not the wide groove hemi race bearings

I found this picture where the oil hole should be located in the upper half of the bearing and not on the bottom:



Source: http://www.dura-bondbearing.com/Portals/3/pdf/Cam%20bearing%20oil%20holeTechnical%20Bulletin.pdf

Found this in an old street rodder mag about the topic:

"On engine blocks that do not feature an oiling groove on the bearing bores, it is vital that each cam bearing is installed in the correct clock-position, so that the bearing’s oil hole accurately aligns with the cam bore oiling hole. If the cam bore features a groove, the bearing should be installed with its oiling hole placed at the 2:00 position (when viewed from the front of the block that features clockwise rotation).

By placing the bearing’s oil hole at roughly the 2:00 position (anywhere between 2:00 and 3:00 is fine), oil is fed into the clearance between the cam journal and cam bearing as the cam rotates clockwise, creating an oil wedge that travels down and supports the cam much better during cam rotation. This forces a superior oil wedge under the cam, to provide oil support at the bottom (6:00) position."

the question is is the oil pressure high enough to work against the valve springs?

about the thrust bearing: just a precaution. another option I know is to slightly chamfer the parting lines of the thrust bearing (from the middle of the bearing to the rear which directs oil to the thrust face).

I just chamfer the bottom half of the thrust bearing shell at the parting line from the oil groove toward the back, to help oil the rearside of the thrust brg.

You might go to www.moparchat.com then scroll down to & click on "circle track chat" & read Sanborns' oiling (& cooling) mods that are in a sticky at the top of the page & see what you think. It's SB orientated but alot is the same. it'll take you several hours to peruse/absorb it all but it is well worth it.