chassis is flexed...consequences???

*my car is a hatchback*
When i bought my car there was a 1/4" gap along the jacking rail on the driver's side and the floor was heavily cracked. I got it welded and since then i noticed the after effects of this: the sunroof has dimples around it, the 1/4 panels have slight bends to them (like they're folded from flexing) and the cowl/hood/trim/fenders don't quite line up correctly and the doors don't quite shut as easily as they should (not lined up correctly). I had a stroked 351W in mind for this vehicle and chassis bracing to keep it from flexing while launching at the strip (i want this to eventually be at least a mid 12 second street/strip car). What are the negative consequences to having the chassis bent like this? Is it even worth my time to put some money into this car? The chassis flex is noticable because it was driven along time with a cracked floor and until i got it, it was completely stock. Keep in mind i don't want to autocross it, i just want a quick street/strip car. All opinions are appreciated, thanks.

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'84 Mustang 5.0 T5, FRPP alum. radiator, 1 5/8 shortys/2.5" offroad-H, Flowtech Warlock cat-back, '88 GT tail lights and wheels, Holley 600cfm, FRPP smog pump idler, no smog stuff, money coming in for more soon