Thinking about this, I've got my 106 with k241 10hp, I use it for pulling heavy loads. Just like stated above, it has no power issues, only traction. Even though it's a smaller engine I've never even come remotely close to stalling it out.
I think you can keep the K301 and use it without issue
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'70 107 with k301 engine swap
'71 106 with 38" deck
'70 147
R with factory replacement k321, 42" deck
'61 Original with 38" timed deck
'63 70 "pinkie"
1863 with 54" deck
'46 Farmall H, '50 Farmall Cub
105 x2 (parts)