I had in mind doing this conversion on my '74 at some point.Best thing would be as mentioned,find a complete car to pull all necessary parts from.You will need to cut out the pillar between the door window and louvers,weld back in the correct longer rain gutter or remove them completely depending on tastes,other than that most everything else should be bolt in as far as I know,and be prepared for rust under insert.

I guess for myself,after pricing all the parts needed I have almost decided that it wasn't the louvers that bothered me so much as all the rest of the SE trim,vinyl top,the exposed headlight grills and bumpers that stuck out a mile.Once I got used to looking at the louvers,I didn't really think they any worse than the cat-eye/Gremlin windows on the 71's or 'helmet head' on the 72's.

I do like the hardtop look as well though on 73/74's...good luck on the conversion,and take pictures if you can.