Being a low mile original car I'll assume you aren't looking for aftermarket upgraded exhaust systems, even though there are a couple of excellent crossflow systems out there that I use and am very happy with. Pypes and Dynomax.
Dynomax offers the transverse mufflers separately, and they have a very nice sound without being obnoxious or overly aggressive, and also have the correct flow path as OEM (Pypes is different) but they are 2 1/2" inlet and outlet.
The OEM system are only 2 1/4" inlets with 2" outlets. If you want to keep those sizes and correct appearance/fit then Waldron might be another option.
They sell just a transverse muffler, said to flow a little better than a stock muffler with internal dimensions larger than stock, and will make them to any inlet/outlet size you want, in aluminized material or stainless steel. However I do not know what they sound like, I've never tried one myself.
http://waldronexhaust.com/cart/index...oducts_id=4689
http://waldronexhaust.com/cart/index...oducts_id=4690