Looks like you've got the correct motor mount but its installed backwards, the back of your engine should be elevated higher. The reason they do this on side engine race karts is so the aftermarket race-style air cleaners and headers will clear the right rear tire.
With a 15 degree angled motor mount like yours, most guys that race these engines only use between 12 and 16 ounce's of oil in the engine. I'd suggest using around 16 ounce's on yours and then check your oil level often.
As far as the seat goes: Some motor mount brands have a side to side adjustment feature to get a bit more seat clearance, but its totally normal to have to move your seat over when installing a 4-stroke on karts like yours. Your kart probably had a much narrower 2-stroke engine with the clutch/chain located on the outside before, so they had much more room to center the seat.
You'll want to get your chain guard, clutch and chain all installed first, and then leave about an inch of clearance between those and the seat to compensate for the seat flexing over a bit on fast left turns.
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