No "Dockbuster" (aka "Direct Reversing) will have a "neutral" as the motor is either running in Fwd or running in Reverse. There is no mechanism for shifting gears in a Direct Reversing lower unit, the engine runs backwards for Reverse.
It's very possible someone took a Dockbuster 800 powerhead and stuffed it onto a Full Gear Shift mid-section & bottom. I did that years ago and found out that the 800 "DR" crankshaft is not broached as deeply as the FGS crank. The FGS lower unit wouldn't go up all the way until I cut and ground new splines on the end of the driveshaft.
After that, everything worked perfectly. If that's what happened, and was done correctly, the only caveat would be that if the L/U ever needed to be replaced, the new FGS L/U would have to have the driveshaft shortened and re-splined to fit. There is a company back in Michigan (as I recall) that'll do this for around $75 but you would have to pull the shaft out of the L/U and send it to them, as they wouldn't be able to do it with the driveshaft still in the L/U.
Anyway, if that's the case not a big deal, but if it's still a true DR motor, they're feeding you a line.
Not that there's anything wrong with a well-tuned DR, in good condition they're a sweet runner. You just have to get used to the way they operate.
Well, hope that helps, let us know how the deal works out.....ed