To answer your original question, I would make adjustments until the prop ( thrustline ) is strait up and down. Perhaps hang a plumb bob just in front to the prop and then measure the distance between the prop tips and the line.

Getting there is another topic. Don’t take your fuel into account, always balance with an empty tank. I personally do everything I can to not add dead weight to an airplane. Sometimes it is unavoidable but there are other things to do first. Being that you are using a multi cylinder radial, I’m going to assume that it has an ignition module. The ignition battery should be mounted as far forward as possible. Your RX battery can also go up front as far as possible as well but that tends to bring along a couple concerns. First is having the two that close together. Some feel that the ignition battery can transfer interference to the RX battery. With a 2.4 ghz system I have never had this happen and I personally consider this a non issue. The second concern is the long wire run to the receiver. For this airplane, as long as your wires are at least 20 gauge you should be fine. 2.4 ghz is a bit more voltage sensitive so you do not want the receiver getting less then 5 volts under load ( my philosophy ). That brings up another option to get weight up front. A second RX battery. A second battery will not only provide you with redundant power but will increase available current supply to the receiver and pretty much guarantee you will not experience voltage dips.

You will gain better CG adjustments by removing weight from the tail ( again my philosophy). Looking at the manual I see one thing I would do right off and that would be yo replace the steel rudder and tailwheel cables with Kevlar cord ( Available from Aerospace Composites Products ). That alone would be a big help as I suspect those 4 cables have some weight to them. I would also move the rudder servo forward. The second thing I would do is get rid of the steel elevator pushrods and replace then with carbon fiber rod ( also available at ACP ). That would yield the largest weight reduction off the tail. Doing this would require attaching some Dubro threaded couplers on at least one end of the CF rod with JB Weld. To be honest, I typically just epoxy a clevis on each end with the servo and control surface being centered. A side benefit of getting rid of the steel cables and pushrods is you don’t have long runs of steel that could act as antennas and create RF issues although that is very highly unlikely.

The final thing I noticed in the manual is the aileron linkage and suggested throws. The linkage IMO just plainly sucks. You will never get the same throws on both the upper and lower ailerons with the kit supplied hardware. Unfortunately just about every ARF bipe I have seen uses this system. In order to get equal aileron throw the linkage pivots must be on the ailerons center. As shown in the manual the lower aileron has it above center and the upper aileron has it below center. The bigger issue for me here is that they show equal throw up and down movement. First off the linkage makes that impossible to begin with but you will definitely want some differential in there. If you use the provided linkage, take your measurements from the bottom ailerons and have the travel 20%-25% more upward then down. This will greatly reduce if not entirely eliminate the adverse yaw the stock setup would induce.

Best of luck!