Should I get my car running driving as is OR

I'm looking at $7,500 to get it running/driving like I'd want (body untouched minus SFC's)- $3,500 bare minimum

the stock 400 BB will not be enough for me coming from a 350hp lightened fox Mustang SO that needs a top end, needs full 3" exhaust, needs the 8 3/4 I have setup and put together, need to have the 727 I have rebuilt, needs new head liner, new windshield (will be under $200 installed as I work at a dealership), need SFC's, IF the rear wheels don't fit need new one's, and there is much more I'm leaving out...

1 thing I'm not sure of IS if the 10" front disc brakes I built for it will handle a 400hp big block..

As for budget - don't have one as in spend $700 at a time every couple months.. plus I sell stuff on eBay and IF I sell my Mustang motor the big block top end kit will be bought