Arca Swiss do make a version of the D4 with a geared pan but it is very hard to actually buy.
https://www.arca-shop.de/stativkoepfe/getriebeneiger/d4-serie/d4/779/d4-geared-pan-monoballfix?c=840
and here
Mit dem d4 hat ARCA-SWISS erneut eine revolutionären Neukonzeption des herkömmlichen 3-Wege Neigers entwicklet. Bei dem d4 handelt es sich um eine…
www.arca-shop.de
The Loctite they use on the newer heads to secure the clamp just needs heating to release so it will be 262 Red or an equivalent, it can be done safely with a soldering iron on the main Allen head bolt, it is commonly used in machinery.
But for the OP even the d4 is at the limit of stability with a 300mm f2.8, 2x TC and a body hanging off it. The Manfrotto 400 is the best of the bunch for that application and has geared pan.
The d4 is great for considered photography like product, architecture, still life etc as the pan (yaw) really isn't difficult to set precisely manually whereas the roll and pitch do greatly benefit from the precision gearing gives for those subjects. For the OP I can see having geared yaw would be an advantage.
As for the levels the d4 has three of them, one tube for each axis on the side and one circular bubble level on the top clamp, I used to set my tripod up by the top bubble level but I now use the camera level on the rear screen and find it to be plenty accurate enough for stitching and even 360º x 180º spherical panoramas.