Count, here are some numbers from My Air Command years: On a no-pod, stripped, inverted-Rotax model, the CG is 5-6" below the thrustline. This is a dangerous amount of HTL, as you have already surmised.
You need to move weights up the move the CG up. The formula for the distance you must move a weight for a given amount of CG movement is
(CG movement)/(weight/gross weight).
Example: You're going to move the pilot's seat (yourself) up. You weigh 200 lb. The machine grosses 600 lb. You need to move the CG up six inches:
6"/(200/600) = 18". You must move the seat up 18" to move the CG up 6".
Certainly switch to a mast that's undrilled at the engine mount/seatback point. This requires new engine mount cluster plates that use bolts that pass outside the tube instead of through it, in a clamp-on arrangement.
Even if you achieve CLT by raising the seat, add a H-stab if your gyro doesn't have one.
I kept the original pump stick but added beefier pivots. The originals, using Oilite bearings through 1/8" aluminum stock, get sloppy quickly.