Although this (IOE or "F" head) conversion is inferior to a complete new OHV head in terms of power, it's still a very large improvement over a sidevalve, and much easier to construct.
Begin with a head, iron is OK but easier with aluminum since the chamber has to be welded. It's important that there be a "window" in the head above the cylinder which is dry (does not include any water or hollow space), since this will be bored straight through from the upper (bolted) surface to the gasket surface to permit the intake valve to open.
The existing head bolt pattern will determine how and where the new intake "module" (self-contained port, rocker arm housing, cover etc.) will go.
There must be oil to the OHV valve gear, so a pressure source must be tapped (like the stovebolt) and a line run up to each module. Oil drain can be done by contouring the "floor" (top surface of the head) with channels to direct spent oil to the "plug" which performs multiple functions:
1. closes off the original sidevalve intake valve seat
2. allows the new OHV intake pushrod to access the intake tappet
3. oil goes down the pushrod hole to the tappet gallery
The new static compression ratio could be quite high, but unless the cam is reground with the intake duration (especially the closing point) extended to OHV standards (no such cam exists) a conservative CR would be preferred to keep cranking compression suitable for pump gas (165-180 psi?).
A Schedule 80 90° "weld ell" should make an interesting start for a module, it's weldable, cheap, has excellent internal shape.
