John - I afraid I can't be much help on the cowling as I have not installed mine yet. I don't think an extension is going to be required if you are using the original style cowling (like me) as none of completed 601/650's I've seen have required it. An extension may be required with the new cowling design, but you should probably talk to Jan about that. I plan on using Skybolts or Dzus  fasteners to attach the cowling also. On the fuel pumps, I would think they would really have to be well insulated from the heat as there is a lot of heated air under the cowl from the engine and leaving the radiator. I would also think the pump that was not being used would soak up a lot of heat with no fuel flowing through it. Firewall would also be the worst place to have an unplanned fuel leak (not that there are any good places.....). 

Just to clarify, the pumps are mounted inline but both feed the regulator with separate lines, not the pump in front.  I could should have made that more clear in my first response.

John, I did it a little different than most others. I have a drag racing background and one major safety item in racing is that you NEVER have the pumps or rubber fuel line in the passenger compartment.  What I did was mount the pump below the floor on the doubler that runs through the centerline of the plane.  The pumps are mounted in-line, one behind the other feeding into the regulator up front behind the nose wheel steering bearing. The whole thing is covered with a 'U" shape cover. It's directly behind the nose gear and below the cowling, so there is not a ton of added drag, but I am a lot more comfortable with all the possible fuel leaks outside the cabin and way behind the engine. For the fuel filters, I used inline stainless steel mesh screen filters mounted in the wings between the tank and fuselage  sides on stainless hose.  They are ran easy to get at thru the fuel access door at the bottom of each wing and compact.