I went through this dilemma last year building my 1981 KLX250. 17.5 inch shocks aren't long enough, you need 18 inch. I bought a pair of progressive brand from the US and modified them to get the correct ride height, I also run them upside down to get enough clearance at the top mount. They now work fine for Vinduro stuff.
FOX Shocks wont fit. The other option are to have the original units rebuilt, unfortunately I sold mine. Ohlins are an option but very expensive.