  Short-lived radioisotopes (SLRI) such as $^{60}$Fe and $^{26}$Al were likely
injected into the solar nebula in a spatially and temporally heterogeneous
manner. Marginally gravitationally unstable (MGU) disks, of the type required
to form gas giant planets, are capable of rapid homogenization of isotopic
heterogeneity as well as of rapid radial transport of dust grains and gases
throughout a protoplanetary disk. Two different types of new models of a MGU
disk in orbit around a solar-mass protostar are presented. The first set has
variations in the number of terms in the spherical harmonic solution for the
gravitational potential, effectively studying the effect of varying the spatial
resolution of the gravitational torques responsible for MGU disk evolution. The
second set explores the effects of varying the initial minimum value of the
Toomre $Q$ stability parameter, from values of 1.4 to 2.5, i.e., toward
increasingly less unstable disks. The new models show that the basic results
are largely independent of both sets of variations. MGU disk models robustly
result in rapid mixing of initially highly heterogeneous distributions of SLRIs
to levels of $\sim$ 10% in both the inner ($<$ 5 AU) and outer ($>$ 10 AU) disk
regions, and to even lower levels ($\sim$ 2%) in intermediate regions, where
gravitational torques are most effective at mixing. These gradients should have
cosmochemical implications for the distribution of SLRIs and stable oxygen
isotopes contained in planetesimals (e.g., comets) formed in the giant planet
region ($\sim$ 5 to $\sim$ 10 AU) compared to those formed elsewhere.
