318 upgrades

Next dumb question is ; what's the best/easiest/cheapest way to lighten my 75 dart-Swinger by 15%, so that the 318 will perform like she be 15% bigger.
It's a trick question; best /easiest/cheapest, as it applies in this context, should never be found in the same sentence.

EDIT
15% is like over 500 pounds.
For a streeter to lose that much weight is no easy task; yur gunna have to make sacrifices.
Like right off the hop, your A/C and P/S have to go, to make room for a bigger/heavier rear-end and a probably, a heavier trans.
Loosing bumpers, seats, and carpeting, in your Streeter are not a great option, nor are lexan windows.
Yur gonna run dual exhaust so that's doubling the weight of exhaust system, and yur gunna run tires and wheels that will likely at least double the weight of stock. And HD springs and shocks will need to be swapped in, which are ........ heavier, again.
>There is a lotta lotta trading going on, and in the end, your streeter is gunna be roughly equal in weight, before and after the transformation. There is only so much you can do with weight.
My advice is to
>NOT choose a 75 Swinger SE in the first place,
>Go find a swb car with big fat tubs.........
>then stroke that 318, and
>run an overdrive with race-gears and a modest stall. >and drive it in a straight-line, until you can afford to upgrade the Suspension/steering/and brakes, etc.
With the stroker being 23% bigger, she'll hardly notice the extra pounds.
>But corners on 205s, even 225s, are not gonna be fun for long. In the back, that stroker is gunna need 275s for straight-line work, and 295s if corners are involved. In the front, 245s are adequate, but putting them on the front is no easy/cheap task, at least not on the factory parts.. I settled for 235s, and let her slide around a bit. I mean speeds are down in the survivable zone, and if yur tires are at least predictable, it ain't so bad. Just keep spare wheels in stock. I use aluminum wheels cuz I can weld the busted pieces back in.
Happy HotRodding.............