Geez, must be frustrating as hell being so close, don't falter now

Have just read the smooth-cast 327 datasheet and sure enough it does mention working in a warm environment and also that moisture may be problematic (but mainly with shelf-life rather than properties)

So, taking that to its limit,.... I know you haven't got a huge amount of time before this stuff starts curing but you could pre-heat the resin and hardener components before you mix (this will reduce the viscosity even more allowing easier de-gassing and also address any moisture issues).

Start off with a 10 to 20 degree centigrade increase and see if your working time is acceptable and of course whether it makes any difference. Also may be worth heating the mould and mixing vessel to match the resin temperature as well as working in a >25 deg C environment.

Anyway, good luck. Sim