You heard wrong, there's NO alteration required. The swap was so easy that my father did the swap all by himself while the car was parked inside our home garage.
The B20A came stock in 85-85 Accords, 85-86 Preludes, 85-86 Vigor, 87-89 Vigor and the 88-91 Prelude, all share the same layout and thus the engine is a bolt on fit.
Parts should be interchangeable with some engines, not with the rest of the B-series family though. (you'll have to check). But the whole internet is full of B20A parts, just look at ebay for instance, parts can be imported without any hassle. The engine doesn't break down so easily so you won't be needing all the pistons, valves etc, just the oil filter and belts which are easily interchangeable with other Honda parts.
However, a D-series will not even be close to a bolt on fit.
