I wouldn't worry about the valve in the older alternator. Plenty of rocker in them to handle steeper drops.
I wouldn't take an addvance as it would feel too bulky in the good Indo waves.
You could also look at used Hellfires if you can find one in a longer size.
Also Simon Anderson Robo molluscs, Rusty big cats and the like since it would be a back up rather than your primary board.
They are rare but come up every so often.
Also check out Michael Cundith for any used boards like his islander or lip hits.
www.mcsurf.com.au/shopping/islander/143/1 They've been used to great success in Indo by older crew.