If the engien really is runnign OK, then there is little you can do short of putting in a bigger cam and/or aftermarket heads. CR might be a bit low though for aluminum heads.

I would say look at things to lighten up the car, it will make it easier to get moving and might even help you out a bunch if you have manual steering. I know it sure made my 69 RR MUCH easier to live with when I was albe to cut some wieght with aluminum WP and housing, alng with a mini starter and ditching my iron intake. Aluminum master is next when the time comes.

Short of that, not much you can do. My RR had more grunt with the 440, but the 383 is fine for my use. Just will never have the pop the big engine did. Of course I get better MPG now...