Please pardon this elementary question. I'm new to this airline.

I have award travel from Seattle to Denpasar, Bali, booked using United Airlines (Star Alliance) frequent flyer miles. The trip goes:
SEA - SFO - on United
Then on Singapore Air...
SFO - HKG (B747-400)
HKG - SIN (B777-200)
SIN - DPS (B777-200)

(The return is somewhat more complicated, with a flight from DPS - BKK on Thai with a stopover there, then home via United)

When I booked the award flights, United gave me assigned seats on the United legs. They did not give assigned seats on the SQ flights.

The outbound will be a long, long string of flights in coach. I'm not expecting an upgrade to anything better (wish I could, but no status) and I just fervently want to avoid getting stuck in a bad seat (e.g. middle, non-reclining, etc.).

Will Singapore Air give assigned seats on a *A award ticket? Do I just call them and try? I'd like to know what to expect before I try that - any tips regarding best time/day to call to increase one's chances of getting a cooperative agent?

Also, Seatguru.com says that SQ uses 4 different versions of the 747-400. Can anyone tell me which they use on SQ001 (SFO-HKG)? I'd like to look at a seat diagram before attempting to pick seats.

Thanks for your help.