I have a new (well about 1 year old, so almost new) Bushy A3 w/ 20" H-Bar and fixed stock. This rifle is great fun to shoot, but I think I'd like to convert it to M4 style. (I'd keep the 20" barrel and furniture in case I want to change back someday). So I came across an ad for a new 16" DPMS barreled upper w/ charging handle, bolt, the whole enchilada for $499, which, given what I've seen lately, seems fair. The ad says "just drop on your pre-ban lower and you're ready to go"... Well here's the question... Should that be telling me something? Are there BATF restrictions against reconfiguring my rifle as described? (I live in DE and could have bought the rifle in M4 config had me dealer had one when I wanted it. In fact, M4 types are sold here all the time). Thanks for any info you acan offer!!