Head Casting Numbers Question

Hi all,

Let me start by saying that this isn't strictly A-body in application, but searching this site brings up more casting number posts than any other, so this seems a welcome topic. I just bought an '86 dodge W-150 for a 4-speed and a freshly built 318 for stoopid cheap. The motor was built 9,000 miles ago by questionable rednecks, sports a "mild cam" lift and duration have yet to be determined, an Edelbrock performer RPM dual plane intake, and Edelbrock 1400 (600 CFM) carb advertised for fuel economy, headers, and flat top pistons. When I bought the truck, I was told it had "340 heads". I thought this was hot air, and didn't really pay attention. I have a single plane Edelbrock, and rebuilt '72 Thermoquad ready to go on this. Before I blindly slapped it on, I thought I'd actually look at the build to figure out if that was appropriate. The heads have no info next to the spark plugs, or casting numbers on the intake runners. There is the time stamp on the #7 intake runner, but it's incomplete.. not a full circle, there's a similar marking on the #5 exhaust runner, that has only two dots and an arrow. Using a mirror after I snatched the intake off, both heads have "348915-A" on the underside. Some searching has brought up that these could be 340-360 heads, and would be "J"s. The weird casting number (instead of "3418915") has got me curious, as does the exhaust ports having the space for the smog hole, but it was either never machined in, or very professionally filled up. So, finally the question. What the hell am I looking at? How do I read the time stamp? Near as I can piece together, these are mid 70's (blank smog hole) 360 heads? any way to tell the valve size without pulling the head? Oh, and which would you guys run on a 4x4 I want to tow with? the T-Quad? Love them small primaries for throttle response and city MPG, but wont fit on the dual plane.. Or the 1400, which seemed to run well enough, and the guy swore he got 14 MPG out of it? Sorry for being slightly off topic A-body guys, but I am building up a '63 Valiant.. Does that count?

Matt