Engine Switch vs. Value

[AAOK]

Brand new here to post, but I've been reading some of the chatter. I have a stock 1969 Mustang Fastback J code 302/C4. I'm planning to make it a Resto Mod staying mostly stock, but with more Horses, lowered, 18" wheels and tires, and custom paint. I have the opportunity purchase a 347 Stroker/C6 with all the good stuff, but am getting conflicting views from the two restorers I'm considering. One says with the Stroker, and all the rest I plan, the finished value will be $35-$40K. The other says for a Resto Mod, the value will be about the same with the stock 302 as with the 347; about $30K. With the 347/C6 I'm looking at about $35K invested in the reto; about $5000 less without it. Anybody have an educated opinion?