I did a quick hack to Tuareg to get indentation working in python-mode
like way. You will find the el file here enclosed.

To autoload I use the following (warning to lisp lovers: this is very
ugly, I'm just getting started with elisp).

(autoload 'tuareg-mode "tuareg" "Major mode for editing Caml code" t)
(autoload 'caml+twt-mode "caml+twt" "Major mode for editing Caml+twt code" t)

(defun start-mlmode ()
    (when
        (save-excursion
          (progn
            (goto-char (point-min))
            (looking-at "(\\*pp ocaml\\+twt\\*)[:blank:]*")
            )
          )
      (caml+twt-mode)
      ;;(tuareg-mode)
      )
      (remove-hook 'find-file-hook 'start-mlmode 1)
    )

(add-hook 'tuareg-load-hook ( lambda ()(add-hook 'find-file-hook
'start-mlmode 1))

Which will switch over to caml+twt mode on opening a file with a .ml
extension only if the first line is:

(*pp ocaml+twt*)

(this is consistent with OCamlMakefile).
Syntax highlighting of comments doesn't work anymore.
Hope this turns out usefull to someone.
Till

P.S. Mike, I sent you a mail about this mode a while back but I never
got an answer. If some lisp addict could clean it up I think it should
go in the distribtion of ocaml+twt.