Have to mention it here: R77.30 is no longer supported, so doing anything with it would automatically render possible TAC involvement null. Other than that, if you have more than one public range larger than /24, in my personal opinion, it is better to handle BGP on a router sandwich between you and ISPs.
You can balance between ISP links advertising single AS with prepends out of a single cluster interface (or bond), but it will be an uneven balancing based on proximity of the destination to one of the ISPs. I suppose you can expand it with second AS and connect it to the cluster using ISP redundancy with load sharing.
Inbound connection balancing or redundancy in this case will depend on the presence of the DNS server on the inside, that will be resolving your public hostnames to the IPs from the proper range, so not optimal.
Perhaps there are better ways to achieve what you are trying to accomplish. Let's see if someone else would chime in.
See this prehistoric diagram of how what I was talking about was once configured: