Mostrar Select (html) con datos a partir de un DataTable en C# & Razor

_Convert.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Web;
using System.Web.Mvc;
using System.Web.UI.WebControls;

namespace VisibilidadWeb.Models.Methods {

  public class _Convert {

    /**
     * <summary>Convierte un System.Data.DataTable a un System.Web.Mvc.SelectList</summary>     
     * <param name="table">DataTable a convertir en SelectList</param>
     * <param name="valueField">Columna a tomar como clave: identificador, clave, ID...</param>
     * <param name="textField">Columna a mostrar: Nombre, descripción...</param>
     * <returns>System.Web.Mvc.SelectList</returns>
     */
    public static SelectList DataTableToList(DataTable table, string valueField, string textField) {
      List<ListItem> list = new List<ListItem>();

      foreach (DataRow row in table.Rows) {
        list.Add(new ListItem() {
          Text = row[valueField].ToString(),
          Value = row[textField].ToString()
        });
      }

      return new SelectList(list, "Value", "Text");
    }
  }
}

Crear.cshtml

<div class="">
  @Html.LabelFor(model => model.griv_idgrupoinv, htmlAttributes: new { @class = "" })
  @Html.DropDownList("griv_idgrupoinv", new SelectList(ViewBag.GrupoInv, "Text", "Value"), new { @class = "form-control" })
</div>

GrupoInvestigacionModel.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Data;
using VisibilidadWeb.Models.BD;

namespace VisibilidadWeb.Models {

  public class GrupoInvestigacionModel {

    [DataType(DataType.MultilineText)]
    [Display(Name = "ID Grupo de investigacion")]
    public int griv_idgrupoinv { get; set; }

    [Required]
    [DataType(DataType.DateTime)]
    [Display(Name = "Fecha de creacion")]
    public string griv_fechacreacion { get; set; }

    [Required]
    [DataType(DataType.Text)]
    [Display(Name = "Nombre")]
    public string griv_nombre { get; set; }

    [Required]
    [DataType(DataType.MultilineText)]
    [Display(Name = "Descripcion")]
    public string griv_descripcion { get; set; }

    [Required]
    [DataType(DataType.Text)]
    [Display(Name = "ID User director")]
    public long user_director { get; set; }

    Conexion conexion = new Conexion();

    public GrupoInvestigacionModel() { }

    /**
    Función utilizada SemilleroController.cs
    */
    public DataTable get_grupo_investigacion() {
      return conexion.realizarConsulta("PR_SELECT_GRUPO_INVESTIGACION ", "CR_RESULT ", null);
    }
  }
}

SemilleroController.cs

using System.Data;
using System.Web.Mvc;
using VisibilidadWeb.Models;
using VisibilidadWeb.Models.Methods;

namespace VisibilidadWeb.Controllers {

  public class SemilleroController : Controller {

    SemilleroModel _semillero = new SemilleroModel();
    GrupoInvestigacionModel _grinv = new GrupoInvestigacionModel();

    #region crear semillero
    [HttpGet]
    public ActionResult Crear() {
      ViewBag.GrupoInv = _Convert.DataTableToList(_grinv.get_grupo_investigacion(), "smlr_idsemillero", "smlr_nombre");
            
      return View();
    }
    #endregion
  }
}