It is not possible to have a failover bundle and use it as a primary unit, if this answers your question. If it is possible to use a unrestricted unit as a failover unit I do not know for sure, but I guess not :-(
If this does not answer your question, can you be more specific on what you want to achieve (what productnumbers you have for example)
The primary unit in the failover pair must have a Unrestricted (UR) license. The secondary unit can have a Failover (FO) or UR license. As far as this condition is satisfied, the software version and the model are identical, itcan form a FO bundle. Please refer to the below url for more info;
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...