When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
We need a stickey with how to convert a 360 to a 390...
Simple version:
Anyway, you need to obtain a 390 crankshaft and a set of 390 rods. You use 360 pistons with the 390 crank and rods to get a good high compression 390.
Post the numbers off each set of head so we can tell you what you've got. Also post the block numbers. Numbers we're looking for are, for example:
Heads: D2TE-AA
Block: D3TE
A great place to get your 390 crank and rods is the junkyard. There's plenty of pickup trucks (usually F250 or F350) out there that have the low compression 390's in them. Find one that doesn't have any spun bearings and go from there.
On the heads: A lot of times the 360 and 390 used the same heads. On late truck motors anyway. But get the numbers then we will know exactly what you have and what would work better.