From what I’ve seen the frame rails are different. Check out real deal steel, they have a 70 to 73 trunk floor/frame rail combo for around $1200… if you get that deep in it, I would suggest you get a body jig to
Keep things straight.

 

Also, I believe the quarter panels are different because of the taillights. That’s getting to be a big job but it is doable.

 

Not sure about the frames. I suspect they'd be different due to 74 being first year for energy absorbing bumpers. Those require a pretty significant mounting surface. Actually the hood, roof, trunk & doors may be the only body exterior panels that intetchange. Fenders and quarters likely different. Quarters as already suggested due to wrap around tail lights. Fenders due to completely different front end style. 70-73 was more square, 74 is much more sloped. Easier to see side by side. Old pic of my 72 and 74 you can see how different the front was. Sorry the 69 gets in the way. Good luck with your project!
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Thank you, I might try and stick with the 74 trunk and gutters. I don't know if 74 rails will fit the 73 trunk panel I bought? I think the 73 bumper bolts to the 73 trunk panel though? I have alot of questions still. I wish I knew someone who has done this conversion. Thanks again.

 

Not sure about the frames. I suspect they'd be different due to 74 being first year for energy absorbing bumpers. Those require a pretty significant mounting surface. Actually the hood, roof, trunk & doors may be the only body exterior panels that intetchange. Fenders and quarters likely different. Quarters as already suggested due to wrap around tail lights. Fenders due to completely different front end style. 70-73 was more square, 74 is much more sloped. Easier to see side by side. Old pic of my 72 and 74 you can see how different the front was. Sorry the 69 gets in the way. Good luck with your project!

 

Where are you located?

 

St. Clair shores Michigan