The honesty of your mechanic is not in question. What you have under the hood is. In the long run, a truck with a stock engine will be worth more than a truck with an small block chevy.
Of all the small block chevy engines out there, the 305 is the worst choice for a swap.
Step back, evaluate what you have, and make a plan to go about fixing it. This may very well require an engine swap, or it might involve running what you have. It seems to me your mechanic is not familiar with the old gmc trucks and wants to do what most people do... make it a chevy. There are plenty of excuses for going this route, but few of those excuses truly have any merrit. The gmc engines are tough and reliable, and contrary to belief there are parts available for them.
Does your truck have a 6 cylinder or an 8 cylinder motor?
