When replacing lintels from this period, it will normally suffice to execute a careful removal of the brickwork above the lintel and then replace the wooden lintels with steel-reinforced brick, which can easily support the few courses between the edge of the window niche and the beam above.
Recommended literature in Danish:
Herholdt: Vejledning i Husbygningskunst (1877)
Kaare Kristensen: Murarbejde (1917)
Byggebogen: Ydervægge, alment (1953)