It might be worthwhile to pick up that $100 engine. I believe you have the integrated head. The earlier 250's had the intake and exhaust non-integrated. You can swap the head over, get an Offy intake, mild cam, Langdon split headers and gain a lot of power.
The tough thing for you is that none of that is available for your integrated head. Changing the head opens up a lot more possibilities for bolt-ons that will make a huge difference.
Lumps and valves could be done before you do the swap. This way you're just doing a little at a time and keeping the monthly budget low enough to keep the wife happy.
...you could make the old lower end into a coffee table...
Mines not the integrated head. That started in 75. I have a 74, so I just made the cut...LOL
