Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
What I've read here in Finlands fb groups it´s 9 times of 10 that people buy these cars and dont wait until the oil is warmed enough and start teasing engine. It takes much more time to get oil temper up than water temp. Specially here were we have 0 to -30 celsius outside temp on winter.
@Ben, if you use the stock case bolts then the main bearing tunnel 'should' be ok but that's not always the case. Particularly if the engine has had a previous bearing issue then this can distort the tunnel so it's worth checking.
The clearance recommendations do tend to vary from one manufacturer to another so I can't give you an across-the-board PTW clearance that will work for every forged piston sorry. You'll likely be in the region of 0.004" but there's some wiggle room in that. We're running perfect skirt pistons in our FA20 but that isn't running yet so I can't comment on the results but the theory is great.