You should never spend money you don't have. Fix the BHG and take care of the engine, upgrade when you have enough money saved up that it won't clean out your bank account. If you take out a loan for a swap and then something goes wrong a little while later down the road, what are you going to do?
Saying your car has sentimental value shows you are not thinking clearly, upgrading your automobile is a hobby, you're spending money that you don't need to spend for simple pleasure. A loan is NOT priceless, and I have no idea what you mean by our small economy. I guess I better go check my supra stocks and see how they're doin.
DonS1mpson gave you great advice, as did lots of others in this thread. I suggest you take a step back and rethink taking out the loan, you will more than likely regret it. But if you don't want to listen to us, have fun being in debt, we'll be here to say "Told ya so" when you realize you made a mistake.