There are very few compatible components between a D3LC installation and a new generation Eberspacher heater unfortunately.

It would be important for you to choose a heater model that could satisfactorily function within a likely 75mm internal diameter ducting system ( please confirm your ducting diameter prior making a buying decision).

The natural successor to the D3LC heater within the Eberspacher range ( and suitable for 75MM id ducting ) is currently the M3 D4R heater.

Please initially take a look at our weblink below for this heater

https://www.butlertechnik.com/item/Eberspacher/Airtronic-M3-D4R-Marine-Heater-Kit-inc-Easy-Start-Pro-4kw-12v/C27

Is your boat 12v or 24v ?

We could also create a bespoke kit for you based around this heater model. If you can perhaps ascertain the worthiness of your existing exhaust, ducting, fuel lines, mount plate for example we could remove from our kit and lower the purchase price accordingly.

Thank you, please let me know if you have further questions -  please email sales@butlertechnik.com