03 620 front fork suspension questions

[bagodoosh]

info:
03 620 with non adjustable Marzocchi 43mm forks
160lb rider, without gear

research:
oil weight: shell 7.5wt OR donax ta (ATF)
donax new name: spirax s4 atf hdx
shell 7.5wt viscosity: 22 cst @ 40c, 2.90 cst @ 100c, 153 viscosity index
spirax: 37 @ 40c, 7.6 @ 100c, 180 VI (10wt)

oil level: .41 liter (also .44) (service manual)
105mm (bradblack)
104mm (darkmonster620)
135mm (ducati.ms member after filling with .41L)
oil level measured with spring out, fully compressed

spring length:
292mm (bradblack?)
270mm time to service (service manual)

spring total travel:
122mm (bradblack)
130mm (?)

static sag:
.25-.33 of total travel = 30-40mm general recommendation

questions:
i am changing the springs to racetech linear rate .85kg/mm (FRSP S3827085)
length: 273mm
minimum travel: 165mm

• what oil weight should i use with these springs?
• what airgap should i use with these springs? (speeddog recommended 120mm for .90kg/mm in another post)
• if static sag is 25mm, to make it 30mm - would i need to add or remove preload?
• racetech springs are shorter, but still above the service size. what should my total spring length be? 292mm? 273mm? or whatever size i get when i take the oem out?
• recommended static & rider sag for this setup?