The published version of the introductory paper says that
Magic is written in C under the Berkeley 4.2 Unix operating system for VAX processors and Sun workstations. The current VAX implementation works only with AED color displays with special Berkeley microcode extensions.
A Sun workstation back then would have been at best a 68010-based Sun-2. The VAX system referred to in the paper was a VAX-11/780.
The introduction to Magic 6, released in 1990, mentions that
Magic runs on a number of workstations, such as the DECstation 3100 and Sun's
SPARC processors. Partial Unix System V support is provided, via the
compilation flags mentioned below. The system also runs on the MacII.
Support for the Mac II was new:
To assist people with small machines (such as the Mac II), Magic can now be
compiled without some of its fancy features. Compilation flags are provided,
as indicated below, to eliminate things like routing, plotting, or calma output.
The build configuration explicitly mentions a number of supported hardware platforms: VAXen, MIPS (in little-endian and big-endian mode), WRL Titans, m68k systems (Sun-2, Sun-3, Macintosh II, HP 9000 series 200/800/820), SPARC, and IBM PC-RT. The build supports BSD-based systems (such as Ultrix), SunOS 4.0 or later (using SunView or X11), A/UX and HPUX.
Since support for smaller systems was new in 1990, I think it’s fair to imagine that only “larger” systems were supported in 1985. (“Larger” taken with a pinch of salt, since a Macintosh II in 1990 would be about as capable as a 1985 Sun-2; but by 1990 the main Magic platform had moved to the MIPS-based DECstation 3100 and SPARC-based SPARCstation 1.) Given the conference publication dates of the Magic papers, in 1984 and 1985, there’s even a decent chance that Magic hadn’t grown much beyond its original systems by 1985.
It’s also possible that the limitations on the Macintosh II are tied to limitations in the hardware platform rather than its performance; PMMU-based Macs running early versions of A/UX (before version 3.0) didn’t support demand paging for example.
I haven’t found details of Magic releases between the system described in the papers and Magic 6, apart from a couple of mentions of the PC version of Magic 4.