There is a lot to properly trimming an airplane - more than we can really cover in a single thread. I recently used Hebert's trimming method. I learned a lot while doing it (and following it to a T!) and have a remarkably straight flying airplane.

Anyway, (this is my opinion) since you're flying a 70 size plane in Sportsman, I suggest playing with the CG before buying tools and spending tons of time on the bench. I think a nose heavy CG is probably the most likely culprit. Most people fly airplanes with the CG too far forward. A CG shift takes a few minutes at the field. You can measure and tweak your airplane over the quickly approaching cold season. The reason I say this is because you could open a can of worms and find yourself frustrated or confused or aggravated. Wings and fuselages can warp and twist, and things aren't always lined up perfectly at the factory to begin with. If you look at the trimming methods, CG is tied to thrust line and wing/stab angles. It takes some time to go over everything and learn the trimming methods enough to start using them properly. Most of them have a very specific order so there is planning involved. I took the time to do this and it paid off immensely I think.

It is true that the '45 and roll' test is limited. But it is something. If you go into a 45deg climb, roll inverted, and your nose quickly drops you know you have a CG or trim issue. The plane should hold a 45 for 'a few seconds' at least and gently start to nose down. It should not nose down fast enough to pinch a loop. This test is very subjective but it will hint at a trimming issue if there is one. If the nose falls quickly, move your batteries back. You will need some judgement regarding how far to move them based on how quickly the nose drops. An inch can be a lot depending on where it is so move it gradually.

If you are that nose heavy, you will find the airplane becomes more 'sensitive' so don't be afraid to reduce your aileron/elevator throws. I moved my CG about an inch one day and had to change settings in my radio (I was a little AFT with the CG, moved it FWD and the surfaces felt less responsive).

It sounds like you took the right points from the other thread. There was a lot of stuff in there - it's nice to see you got some good knowledge from all that.