Well, I am going to agree with Gregg. My .060 bored 218 had the dual Offy intake, cast iron headers, HEI dist and I though it ran pretty good. Bought a .030 bored 230 from a guy on the HAMB who pulled it from a 57 model to put in a 318. Broke a valve in the 218 so I Swapped over all the "speed parts" to the 230 with the addition of an Edgy head.
I have not timed it in the 1/4 or put it on a dyno, but I can tell you from seat of the pants that there was a VERY definate, noticible difference with the 230. I did not have the Edgy head on the 218 so how much difference it would have made to the performance of the 218 I do not know. I just know that were I in your shoes and I could swing it financialy, I would swap out the rear for something more drivable then swap to a 230 in a heartbeat.