I would recommend a boom or seat that allows some adjustment. It takes a while to configure a recumbent, in my opinion. I ride a RANS Rocket and it took awhile to get it set in place.
Another option is to ride some bents and try to get the measurements once you feel comfortable.
On the Rocket, it is 13 and 3/4 inches from the front of the steering tube to the back of the bottom bracket. If that is any help.
Just my $.02