Go with the A3 flat-top, JH, you'll have a much wide choice in optics and can always get it w/ the DCH (detachable carry handle A2 sight).
FWIW the best way to mount an Aimpoint on an A2 model is using the ARMS #39A2, with the Aimpoint setting on an ARMS #22M68 mount, (if you decide against my above suggestion)
And yes there is a mount to put the Aimpoint on the handle, unfortunately it'll be SO HIGH you'll not get a good cheek weld with it up there, which is why ya don't see many going that route....
As to the pre-ban issue
www.ar15.com/content/legal/serialNumberList.html this link will take you to the "Information" area here onsite (see above).
Per the law your pre-ban lower must have been assembled as a "complete rifle" prior to Sept. 1994 in order to be a true pre-ban, not subject to the AWB.
You need nuthing other than the serial number for the police which for the most part wouldn't know their derrier from a hole in the ground about this issue, but the BATF is different. They may require proof in the form of dated material or notice from the maker of the lower that is is truly a pre-ban especially if the number is close.
Read the info area for more complete information, see "Pre-ban More than a Date"....
And stick w/ the flat-top you'll be glad ya did........
Mike