The pipe, ramvalve, and rejet will make a big difference. The aluminum flange isn't really a performance mod, it will help if you port and polish since it is already pretty much "polished" on the inside. I just put one on my bike from Eddie Sanders Racing. The stock flange didn't seal worth a crap with its one metal split ring, the aluminum has 2 rubber like gaskets and seals like a champ. Is your 250R the one that was restored on Desert Union?
1985 ATC250ES
1985 ATC250SX
1984 ATC200S "Little Red" - Trailer hitch, Hondaline: Front and Rear Racks, Cooler Rack, Tripmeter, HL Grille, Rubber Footpeg Covers, Mudflaps.
1985 ATC70
2008 CRF230L - Dual Sport
2016 TRX500 Foreman Rubicon Deluxe