I'll stick my neck out and say that if you can get $1500 for even a running 8BA flathead, you are doing well. The big problem with these motors are cracks - through valve seats and down the cylinder bores are the two major areas of concern. All it took was one overheat. Many folks will want some reassurance that these motors are in good shape and without those cracks. The cracks can be repaired, but it's fairly expensive these days and not many shops have the tools nor even a clue as to how. Then there is the cost of 'speed' parts in relation to the amount of horsepower potential. Your choice of a new crate 351W - a good one. You start with more cubic inches and more horsepower then the flattie will ever make right out of the box plus have the advantage of many years of improvements with metallurgy and air flow design.