I flew an Airfast HS748 in the early 90's and remember their Dak in the pre dawn at Seletar with a foot of blue flame from each engine. A beautiful sight. The plane hardly flew except for the occasional Dart engine ferry as it was regarded as the boss' toy. I did try to put together a business proposal to fit the a/c in 1940's style and fly tourists linking in with their Orient Express journey in SE Asia but Airfast weren't interested.
Is anyone in contact with Seletar based pilots of that period (Suryanto, Arnold etc?), maybe you could pm me if you have an email for them.