Is that drag kart option an extra long Junior Dragster type like Tyler's? If so it doesn't seem like its long wheelbase would be as responsive for a kart built to mainly be a drifter. I don't know, Are drifter karts usually extra long like this?
On the other hand that Kohler is probably way too large in physical size to hang off the side mounting position of a modern type race chassis. As far as weight goes I had an engine approaching 100 lbs. on the side of my race chassis, I weigh 230lbs and with my seat moved left-word (for clearance/balance reasons) my kart with 40mm/triple axle bearings did just fine with all that weight.
For a drifter, I'm thinking another option you should consider would be an older 70's style (rear engine) race chassis. Its rear frame section would already be designed/braced for a rear motor mount, that could then be fairly easily enlarged and centered to place all your engines weight dead center for more predictable R/L drifting compared to a side mount kart. Those older rear engine race chassis can also sometimes be bought much cheaper. Many of those older race chassis were mighty fine karts as long as you weren't too dang tall like me...
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