ok, this is what i have come up with as a good budget build for my car.
I think everything you've suggested will work out fine. I don't have any criticism of any of your ideas as nearly all of them are exactly the way I would do it.
I especially applaud your idea of a 904, and a B-body 8.75" rear end.
If you stick to your guns, I think it's a foregone conclusion that you'll wind up with a high 12-second car.
Having said that, and playing the devil's advocate I have just a couple of thoughts I'd like to suggest as POSSSIBLE alternatives to what you're doing.
1. A Professional Products "Crosswind" intake is a bald-faced Chinese copy of an Edelbrock Air Gap, but is about $100.00 cheaper. If money is a factor and you have no problem with buying from a manufacturer that uses Chinese labor, that would be a cheaper alternative. I am not sure there is any difference in the performance of the two. That's a choice for you to make.
2. There are some advantages to utilizing a Magnum 360 block over an L-A, and some disadvantages. The advantages that are obvious are the hydraulic roller cam that they use can be ground to include quicker lift rates than a flat-tappet cam, and make more power without getting into driveabilty issues due to excessive duration and overlap. By that, I mean, if this is a daily driver you're building, you can get the same performance with a milder duration grind if it's a roller, due to the quicker lift ramps. The other advantage in the cam department is the zinc issue that has been foisted upon us by our wonderful government by taking all the ZDDP out of the oil.
That has created serious cam-longivity problems for flat tappet cams and lifters, that rollers don't suffer from.
The single downside to roller cams that I know of, is that their initial cost is higher, and the lifters are more expensive. I realize that can be a killer consideration for anyone on a budget.
The Magnum heads may be (I said MAY BE) better than the J heads in terms of flow, particularly on the exhaust side. Different sources have different opinions on this.
I would definitely check out a Magnum "core" and investigate the cost of a cam package, keeping in mind the negative aspects of flat-tappet cams in todays's zinc-starved lubrication world. You should only have to buy the roller ONCE...
It's possible to get a late (1986?) L-A motor (pre-1992) with roller lifters. If you like the L-A heads better, that might be a way to have your cake and eat it, too... but, I'd definitely look for a way to get roller lifters into this new engine. More money, yes, but definitely worth it, in my opinion.
Engine Quest has some VERY reasonably priced cast iron heads that flow like crazy (supposedly better than the M-P "R/T" head) and are available from a variety of sources, including Hughes. The brand new MOPAR ACTION has a really informative article on these and other small block heads in its latest issue (just got mine in the mail, yesterday.)
Good luck with your project; any way you go will be fine. You really can't make a mistake with a MOPAR!!! :cheers: