being a business head, I'm all for cost vs effectiveness
if you got the shell, and got the engine for free, and put it in and made it work, grats for you dude
even if it'll be slower than hell and probably won't make it past 100mph at the moment
but seriously, if you're going to build a performance engine, I suggest you drive this with the 5m, and spend your hard earned cash into the 7m that you pulled out, make it fresh, rebuild all the internals, put in a great turbo like a GT35R and save your self alot of money and problems later on down the road
in the end, it's your money, we can only make suggestions, although SOME OF US here are more passionate about it than others
good luck to your build