I thought, from your original picture of engine, it may be a mix.
Exhaust stubs are up to K6 as K7 and F2 use the opposite and include the flanges in the pipe with collets to secure. The two systems are interchangeable so doesn't definitively make it one or the other.
The front of the cases look painted aftermarket rather than factory where it's peeling off, along the front of the head too.
Oil filter looks painted, but it's got the F2 only sandwich plate behind it, with extra cooling fins. Again will fit all years I believe, just has the plate plus means of fixing.
F2 head has larger fins across front, plus bigger valves recessed into head further to get them in. Also higher domed pistons to take up extra volume from combustion chamber shape. And different cam.
Carbs, as you've spotted seem to be earlier and not the PD accelerator pumped type of F2.
F2 and K7 were paired for bottom end of motor and both have increased sprocket output bearing to take loading from bigger final drive chain. K7 was silver so could be a painted K7.
It could be F1 motor entirely with F2 filter plate fitted. F2 should be black on the inside to be genuine.
If dismantling the motor, take care to record what they've done with the gaskets, o-rings, seals etc for head and barrels. If they are mixed here you need to know as F2 deletes 4 oil drain holes from head and has different arrangements to the others. Not fixings but sealing of oil ways.