You made 3 posts in a 10 hour period, its a weekend, not all of us live on these forums 24x7. If you want that kind of customer service I’d be glad to sell you a support contract. 
There was a previous post on this exact issue, answering your questions here:
http://forum.mikrotik.com/t/1-1-nat-help-when-behind-a-nat-router/1735/1
Here’s some more information you can find from a simple search engine:
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094adb.shtml
http://www.sjdjweis.com/linux/proxyarp/
Since all of my client public assignments are using a MT assigned IP as their gateway I could just use proxy arp on one interface right?
If I understand your network configuration correctly, yes, but it all depends on what you’re trying to achieve, refer to the previous mikrotik forum post.
Couldn’t I remove the bridge and just use two Ethernet interfaces; one external WAN and one internal and just enable proxy arp on the external to let the WAN side ISP equipment know of my public IP MAC assignments?
Yes this is also known as routeing and is highly recommended because it reduces broadcast traffic by shrinking collision domains and allows more control over what gets forwarded across your network. Rather than a bridge, which just stores and forwards any and all packets, and not to mention broadcast packets which get sent to every host on the bridge.
For a more detailed description of Proxy-arp refer to RFC 1027.