Your boat should be fine as long as it is in good shape and you pay strict attention to the weather and your fuel. I kept my old 204C in Niantic back in the mid '70's and fished south of Montauk and Block Island several times in that 20 footer.
The trick was to pick perfect days with variable winds in the forecast and to run with a buddy boat. There are often periods of calm weather in August and September when the fishing is best out there. Try to run north of Montauk shoals or it can be pretty sloppy even on a good day. Otherwise, getting through Plumb Gut is the roughest part of the trip.
The Butterfish hole is only about 15 miles off of Montauk, so if you run into unexpected poor conditions, be prepared to slogg over there and wait things out for as long as it takes. Carry an EPIRB and the appropriate emergency equipment must in case.
Those distances seem short not compared to the 50 mile runs each way that I often to do in the GOM these days. But I don't have to deal with the tide rips anymore.
