If you have the room series installation well definitely provide more heat ,my Maule has a series setup and has the best heat of any single engine plane I'ave experienced. I hope I can get as nearly as much in my 8 project.
If room under the cowling is lacking try packing some corse stainless steel wool in your existing heat muff . This does 2 things to help , adds more hot surface area and slows down air flow rate which makes the air much warmer .
The Best Government is less Government
Maule MXT-7(daily flyer)
Raidial RV-8R Ephanage Done, Wings Done, Fuselage underway