Have you considered re-valving & new springs on your front ATC250R forks? A lot can be done with the OEM Forks first. BDT Motorsports has done a few Conversions using CRF, YZ as well as other inverted forks for ATC250R's, however; not all users end up thinking the switch to inverts was worth the effort or cost. For technically challenging MX tracks maybe, for TT, FT, Woods....IMO NO.
Take a close look around, reach out to David Ham who uses and has run both OEM and Inverts; David is one of the leading Trike Riders & an absolute 'Beast' on a Trike winning over 5 series in 2018 from AZ to CA, including 100 mile Desert races on his BDT261CC ATC250R...one of the best to give you an honest opinion on Inverts vs re-valved/new spring OEM Forks.
I & the BDT crew will at your WALDO Nationals March 1st/2nd...stop by and say hello, we can discuss engines, Pipes, caburation, Intakes, suspension and Trike Racing.