Lefty:
You might check this out about your choke question.
I was into one similar awhile back that was suppose to use either the Walbro LMT or the Nikki carb and the choke would not operate as intended when the throttle was fully advanced and the set-up looked very similar to yours. The lever on the backing plate with the throttle slider would not quite push the choke linkage far enough forward. I think i see on your a small machine screw with a 1/4 inch head, Removal of that screw will allow more travel of the plastic slider to allow the choke lever to be pushed forward. Maybe the small machine stop screw was installed for some other type of linkage??? If you do not know what I'm referencing, just remove the throttle plate from the engine and you will see the mechanical operation as the throttle plastic piece is moved back towards the rear to apply choke and throttle. (the engine linkage chokes at wide open throttle) Removal of the machine screw just above the plastic slider at the left end upper side will allow the plastic slider and the choke linkage arm to travel further and push the choke linkage. The machine screw is stopping (limiting ) the travel of the choke linkage arm behind the plate. The metal arm that pushes on the choke linkage wire
can also be bent easily if more or less choke is needed.Next about removing the keyed rims on the rusted axles. First do not hammer on the rims or you may ruin the Xmission.
I have a OTC 522 T bar type gear puller, (If you have a welder you can make such also) or HF may have a cheaper equal)
The bar section is 8 inches long and will reach across and rest on the outer edge of the rim to aid in pull alignment, get two 3/8 inch by 6 inches long machine bolts and flat washers for use at the T bar end of the bolts, drill a small recessed dimple hole about 1/4 inch dimple size in the center of the axle to help hold the end of puller bolt centered.
Jack up the tractor's rear and place it on blocks.
Install the 3/8 puller bolts through the rim holes.
Tighten the center puller bolt and
gently tap on the end (like pulling a flywheel, then re-snug. Do not hammer hard or you may bulge the end of the axle and do not use rotary impact tools when tightening. Go by feel. Also watch and do not deform the rim where the puller bolts are pulling.
Do not apply excess force, the rim will remove by slight pecking the center bolt or use a propane torch and heat cool the rear axle portion of the RIM. A rule of thumb when heating is stop the heat when you spit on the metal and it spits back. (heat/cool is your friend here, but heat/cool usually not needed on these)
If the rims do not have the two holes for the 3/8 bolts drill them yourself aligned so as to be axle centered crosswise. (not all lawn tractor rims have the two holes in the outer edges of their rims)
Not a fun job. Patience is your friend here.
Once removed use some sandpaper, clean the axle then apply Anti-sieze to the axle before re-installing.
Damn shame that factory would not spend 2 cents on anti-sieze when new.