Tuning??
If your 100% thinking it needs a good tuning then your far better to tune it and sell it that way. I would think that would bring you more money running and tuned not "I dont know whats wrong but it wont start" and ask a fair running price for it. Ive watched these on Ebay and one here and theyre going for 300-450 running in top shape. There is also another 4.6 on this forum for 375 and thats been listed for a bit and have seen a price drop from him already. Not knowing whats wrong with the motor and chancing its either junk or something simple like maybe a bad plug or bad hoses etc. is a chance not to many are willing to take for that price. Ill offer you 225 shipped as I would consider it a roller and maybe a junk motor or maybe not. If not good luck with the sale.