JUCA does NOT presently charge extra for the modifications to the firebox structure for an arch-top fireplace. HOWEVER, keep in mind that the door assemblies for an arch can generally NOT be any stock-sized doorset, meaning that the doorsets therefore need to be custom-made. The ones that are available tend to be about $400 (or more) higher than similar rectangular (stock-sized) doo assemblies, so the overall cost for the F-9A with arch-top door appearance is likely to be several hundred dollars higher than with rectangular doors.
In the case of the JUCA Double-Sided F-9AX unit, it is possible to select an Arch-Top on both sides or on only one side, while preserving a Rectangular appearance on the other.
Of course, if you are also going OVERSIZE, then the additional cost for extra material would apply, along with the likelihood that larger doorsets will cost more!
The JUCA Home Page is at: http://mb-soft.com/juca/index.html
E-mail to: JUCA1@mb-soft.com