If it runs good and needs nothing.... $200 for a running motor is a good deal. Sell off your 318, hunt down the parts to change it over to a big block, and swap it in. Drive it, and build a 440 later if you want.

Personally I'd find a 360 and drop it into place. The money you save on a BB trans you could probably locate a running 360 or donor car/truck/van...

Just be careful... it's a slippery slope. My 318 was in really poor shape and somebody GAVE me a 360 Volare wagon. My weekend/low-buck swap spiraled WAAAAY out of control into a rebuilt motor and trans and over two years of time and saving.

And remember.... there is no shame in a Satellite. They all don't have to be turned into RR clones...