I don't think we'll have to worry about the 250/292 stuff fading away any time soon. The earlier Stovebolt and GMC stuff is still relatively easy to find after being out of production for over 50 years now. The 4200 engines are still too new to worry about them being difficult to source parts for the next 10-20 years. The interest is what stimulates the demand for parts and production numbers are just too high. Just look at the Model A engines and Flathead Ford stuff. 80 years since the Model A and T engines have been produced and you can find anything for them still including brand new aftermarket blocks and heads being made currently. There has just been very few engines made in the last 100 years that you can't get most anything for today.
