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don't forget you'll also need from 300 (in addition to parts you listed):

  • crankshaft
  • connecting rod
  • piston
  • throttle-body w/TPS & MAP sensor
  • injector
  • IACV set
  • ECU

A simpler solution may be to swap 300 engine into your frame. I've seen this done in couple hours. Rather than the weeks it'll take you to pull 250 engine, disassemble it to put 300 parts in and put i it all back together
 

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I went through a lot of posts regarding this exact topic, I know how most of them seem to say its worthless and a waste of time...
Yes, it can be very valuable learning experience. About 35-yrs ago, I blew up engine on my 1st bike, VF500F. I had particularly difficult semester at school (O-chem), and didn't have time to ride my bike. Left it parked for 6-months and one of carbs clogged up. When I did get around to riding it, lean mixtures in cylinder with clogged carb melted hole in piston and snapped con-rod. All estimates and advise was to swap in new/used/junkyard engine, but I didn't have $2000-2500 to do that.

So I figured I'd tear engine apart and replace just piston and con-rod. While apart, I had cylinder-head shaved to increase compression and port/polish intake & exhaust tracts. Took me couple weekends, I learned A LOT and had better performing bike for only couple hundred bucks instead of thousands! Still have this bike today! :)



At another time, I took it completely apart and painted frame black. Much better looking.
 
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