This group of designs present an alternative simpler scheme for the opera house. Sheppard notes similarities between SM Adam volume 28/25 and Novosielski’s executed design, raising the possibility that he was at least aware of Adam’s scheme. Similarities between the two plans include the shape and formation of the auditorium; the depth and sightlines of the stage; the introduction of a gaming/assembly room to the north-west of the auditorium; and the positioning of the staircases. We also see the inclusion of a painting room to the south-west of the stage, presumably for the construction of scenery.

Bolton suggests that SM Adam volume 28/25 is wrongly inscribed, and that the design is in fact part of Adam’s scheme for Parliament House, Edinburgh. Sheppard, however, notes how Adam’s designs for the opera house, in particular those for the Pall Mall (south) front, (SM Adam volumes 10/100, 10/107-108, 28/16 and 47/2), are stylistically similar to Adam’s public works in Edinburgh, with particular comparison to his scheme for the University. The formation of the east elevation in SM Adam volume 28/22 does not follow that of either of the alternative plans (SM Adam volumes 28/23-24). SM Adam volume 28/24 is the closest in design, but has fewer bays forming the central block, and the addition of paired single-bay porticoes at the north and south ends. SM Adam volume 28/25 does, however, follow the formation of the central thirteen bays of the more extensive scheme (SM Adam volume 47/8-11). Furthermore, the use of scrolled hearts enclosing anthemia follows an ornamental motif used elsewhere in the scheme, particularly in SM Adam volume 28/16, and most significantly the use of musical motifs for the statuary compositions would indeed suggest the design was intended for the opera house.