Might depend on what you are going to do with it.  The G 21 has really only one usable purpose in CL and that is combat (Nostalgia?).  In that case you are pitching that PDP carb and replacing it with CL gear.  If so ......  Maybe $75-$125.   If you are going to use it as some sort of RC engine then who knows.  There would be a lot of better choices for that.  It was a great engine but will likely need new bearings in the near future.  They used brass race bearings, open style.  Nitro eats brass in short order.

Dave

Might depend on what you are going to do with it.  The G 21 has really only one usable purpose in CL and that is combat (Nostalgia?).  In that case you are pitching that PDP carb and replacing it with CL gear.  If so ......  Maybe $75-$125.   If you are going to use it as some sort of RC engine then who knows.  There would be a lot of better choices for that.  It was a great engine but will likely need new bearings in the near future.  They used brass race bearings, open style.  Nitro eats brass in short order.

Dave

FWIW PDP is nothing to do with the carb, it is "perry directional porting"
There is a description of it in this review of an ST60:

http://sceptreflight.com/Model%20Engine%20Tests/ST%20G60%20FI%20ABC-PDP.html