System i Entitlements (urgh!) Question on 270 to Power 6 move

We are still on the road to replacing our old 270 with a bright shiny new
box but confused totally as to what the process would be to move our
licenses from the old box to the new Power 6.

Scenario:
Old 270 V5R1 minimal software packages. Never on software maintenance,
still on hardware maintenance.

New 8204 P520 at v5r4. Planned to be on software and hardware maintenance.

Conversion scenario:
1) Install new box
2) Migrate user ids and configuration for printers etc.
3) Update system software
4) Move ERP system to new box for testing and upgrading (1 to 2 months)
5) Move ERP to new system permanently go live

The pricing is about $6k different in buying all new software and keeping
the old box with valid licenses on both. If we transfer licenses /
entitlements we obligate ourselves to stop using the old box, which we would
eventually anyway.

The question: In the transfer scenario how long do you have to transfer
licenses? I am under the impression it is 14 days. I also realize we can run
the new box for 70 days without permanent keys. Is the a legal way to have
60 days or so time to move off the old box for good. The OS continuation on
the old box for a month is about $2600 so obviously the new licenses method
seems more cost effective since we still can keep the old box live.

Anyone have a definative answer to what the timeline criteria actually are
and how much of it is formal/informal. Would love to do it right!

Thanks

Konrad