  (abridged) We present new Keck images at 0.9 micron and OVRO 1.3 mm continuum
images of five Class I protostars in the Taurus star forming region. We analyze
these data in conjunction with broadband spectral energy distributions and 8-13
micron spectra from the literature using a Monte Carlo radiative transfer code.
By fitting models for the circumstellar dust distributions simultaneously to
the scattered light images, millimeter continuum data, and the SEDs, we attempt
to distinguish between flared disks, infalling envelopes with outflow cavities,
and combinations of disks and envelopes. For each of these circumstellar
density distributions, we generate grids of models for varying geometries, dust
masses, and accretion rates, and determine the best fits by minimizing the
residuals between model and data. Models incorporating both massive envelopes
and massive embedded disks generally fit the imaging+SED data best. Implied
envelope infall rates for these models are consistent with infall rates derived
by previous investigators, although they are approximately an order of
magnitude larger than inner disk accretion rates inferred from recent
spectroscopic measurements. In addition, the disk masses inferred from our
models are close to or larger than the limit for gravitationally stable disks,
indicating that Class I disks may undergo periodic episodes of enhanced
accretion, perhaps as a result of gravitational instabilities. An important
caveat to these results is that in some cases, no single model can fit all of
the imaging and SED data well, suggesting that further refinements to models of
the circumstellar dust distributions around Class I sources are necessary.
