Chrome 20's would look nice; care to elaborate on any of the steps you took, whose kit/parts you used, etc? I've been tempted to bag my '68 Coupe. Yours looks great!
Something to keep in mind when choosing aftermarket wheels: the width of the hub on the '68 is VERY wide; I tried mounting a set of 17" Boyds on mine that used to fit *perfectly* on a full size Chevy truck; the dust cap hit against the center cap on the Boyds in a big way; no way to avoid it except for maybe longer studs and wheel spacers, or same-pattern adapters used as spacers - then of course that can lead to other clearance issues. Probably won't run into this problem with 20" chrome wheels as most designs I've seen have a lot of center cap room, but it will likely be a problem on any billet wheel similar to Boyds.
Also, the edge of the rim (17x8) was rubbing against the upper ball joint! So choose your wheels carefully; make lots of measurements, go with someone local so you can do a test fit.
Oh, also you'll probably have to remove the little bolt on the rear drum that holds the drum secure. Shouldn't cause any ill effects (since basically every other car made with rear drums just lets them ride with no extra securing other than the wheel) but if left there it will keep the wheel from sitting flat against the drum.