413 Big Block

Seemed like the OP was looking to maintain the 413's low compression, so it seems to me this would be the ONLY time a 413 might just be a good idea. Of course, as Jim pointed out fitment is your biggest hurdle here... and the fact the thing was stored outside under a tarp. If you could just throw it in and fire it up or even rering, bearings and hone, I think it might be a fine choice. But that's not the situation here.