That looks like the standard 390 truck setup. Dished pistons with a lot of deck clearance.

You'd definately gain a lot of compresssion with the Silvolite 1131's.

If you go with the 1131's, you should go with the Crane 343941 cam. You'll definately have the compression for it. I run equivalent compression forged pistons and the 941 cam. So far it doesn't ping on 89 octane. Of course I did polish the combustion chambers and that helps a lot.

 

The 1131's sound good but I'm kind of wanting to stay on the safer side. I'll be towing regularly (trailer and 4500lb jeep) on very steep grades, so as to avoid any problems with pinging I should probably stay in the 9.5:1 range. This isn't going to be a hot rod, more of a purpose built puller.

 

Actually, since the silvolite pistons have a 1.76" compression height instead of the 1.776" the original car 390 pistons had, and that the aftermarket TRW forged ones have, you'll likely wind up with 9.5 to 1 compression with the 1131's. 1130's would likely get you 9.0 to 1.