Dave Bushell is entirely correct, well spotted that man! I’d forgotten that important point despite having been tinkering inside my engine’s big-ends within the last month.
Wots a goldfish? Told you I knew nuffink! I’ve just trotted out to the shed to have another look at my DPY engine after that faux pas! Looking a twit just once a day is quite enough thank you . . . !
On the premise that the screws are less expensive and certainly easier to make than a cylinder block the answer would be to cut/grind enough of the screw heads away to get them past the crankcase door lips having first made sure that they are loosened in order that the remains can be removed without further grief! There is enough room for at least one full turn so the full circumference of the heads can be made accessible and that should also be enough to gain the room tuck some protection for the big-end side plates under the heads. Even if the side plates were brand new they too are more easily replaced than the block and should be considered “collateral damage” in this instance, if not new they quite probably will need to be replaced anyway.
Despite the above seeming to be a classic case of one step forward and three back I still consider that gaining some, even if limited, potential independence of the cylinders to be worth it. The ability to mount an assault on one bore at a time will surely pay in the end as well as eliminating the big-ends as a source of stiffness.
Preparation is all as Dave Bushell’s remark proves only too well. The spirit of Professor Sodd is alive and well and is lurking close by! Do some dry runs and remember the old toolmaker’s addage; “Measure twice, cut once!”