There shouldn't be a problem. The 28 models had higher mounting pads on the front crossmember and if a later body is installed the body must be shimmed up higher for the hood to line up. With a lot of shimming I was able to install a dec. 30 pickup cab and bed on a nov. 28 frame
Purdy is shimming the late (30-31) body to make it line up with the higher radiator mount pads of the early (before October 29) frame.
You want to install shims on your late frame radiator mounts to match the early body - which is what Pluck describes.
I have a "transitional" frame (stamped about November of 1929) which I plan to use for the next 1928-9 Model A I will build from parts. Ford in that timeframe and beyond in the parts book actually called out "shims" for this use, and the other parts. If you see the Service Bulletins from this period you can see the shim required thickness - and the additional square sheet rubber piece. The bolt is a little longer too IIRC.
As to putting a late model body on an earlier frame - you may end up drilling holes. For replacement parts Ford generally followed a "backfit requirement" (with the exception of designated "AR" parts which were special and kept in stock because backfitting was not possible or uneconomical to maintain) so that parts inventory could continue to be used going forward. But backfit CAN mean "field modified" by drilling or adaptation for the service groups. And I think the later bodies are not all immediately mount on earlier frames, or visa versa. You may end up field modifying.
But take heart - Ford did consider that the modification was within field service capability - and likely yours too.