1st, do you have tools?
2nd, get a JTR book if you are going V-8, read it 10 times, then read it 10 more, keep it next to the toilet ( I did)
As far as suspension, this is the first place I start, given the car is running.
Do you really need the coil overs or just WANT coil overs? I'd go with a set of new springs and struts. This is an easy way to become aquanted with the car. Get a bushing kit, ball joints and tie rod ends, you;re not a "real" z guy until you do the lower control arm bushings, period
The v8 swap isn't that hard. I had not spun a wrench in years before I started doing my conversion just took my time. As far as engine, are you going crate or build? If I could do it again, I'd go crate. You don't really need 400+ HP (you may want it but not totally necessary, more torque= more stress on parts= breakage.)
Or LS engine.
Finally...if you really need new floor pans, I'd find another car. If the pans are bad the frame rails are bad, more than likely the firewall and where the TC rods connect are bad too. To weld this all up (assuming you're having a shop do it) it's going to cost you, quite a bit. I would figure with pans, frame rails and some bad dog sub frame connectors + labor. I think you'd be in the neighboorhood of $2,000 (parts $459 at the ones I just looked at. Unless these can just be patched, I'd have to see to know
Fender flairs, have them cut you're fenders while you're there, probably run you another $400. So based on this you'll be in it for around $2400+/- just to get the car solid.
Just talking from experience. As stated above, if you're going to keep the car, start with the suspension.
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