Small Block Questions

I have a 1976 B-200 Van that has a 318 in it.
It only has 58,000 miles on it.
I redid the valve seals, double roller timing chain, 4bbl intake, new Summit cam/lifters/springs, and a new radiator.
Should I pull the engine before I send it to the junkyard, as nobody seems to want the van?
What Heads would be on this engine?
Would they work on my 340 with 13-1 pop up TRW pistons?
The X-heads that are on the 340 are in need of a valve job, and maybe this is a cheap alternitive. The X-heads have also been grooved to hold a steel o-ring to aid in sealing.
Would the 318 heads hold the compression with out o-rings, and what would be a good gasket to hold the compression?
Thanks
Norm