Hi guys. I'm thinking of putting together a motor for my Scamp. It's just a driver that handles well but can't get past anything. A stock 318 just no power.
I have everything to support a decent little engine but was wondering which of those two to use. I am looking for 350 hp or so.
I know both these motors have roller cams but was just wondering which one is better to use and why. I have intakes for both of them.

99 all the way. More compression, better flowing intake port, 10 valve cover bolts, dry exhaust bolts, higher ratio rocker. And that is without changing anything else. A piston swap can get you good quench very easy in addition to more compression. They have a waaaaaay better chamber that will take a lot more compression.

Aren't the carb intakes for the Magnum motors kinda spendy?

They're both roller cam motors and you can run Magnum(EQ) heads on either one. If your just going to buy it and install it then the 99 for sure. The EQ heads can be had with either LA or Magnum Intake bolt arrangement.

The magnum air gap is only a few dollars more than the LA air gap.

If you swap heads and give them both the EQ the magnum is still better because the pistons are lighter and will give you a tad more compression as well as a thinner, lower friction ring pack.

The heads can be re-drilled to use any la intake. The 99 will need to use an electric fuel pump unless a cam change, then a timing cover change. A 5 pound electric street pump should work fine though.

If you have AC then the magnum airgap is a PITA. Water outlet location is right where the compressor would be. Bypass hose fitting is pointed in a different direction, but if you use the magnum water pump you'd probably be ok.

Be easier to redrill the heads to take an LA intake than try to make LA accessories work on a Magnum.

Why not use the WHOLE 360 magnum, SMPI and all? I've thrown together some for me, some for friends....awesome outcome.

Rick

I was planning to use a 904 with an aftermarket 10 in convertor. How do you use it with the factory flexplate and crank sensor?

How do you marry this combo to factory AC systems?

If you only want 350HP and you really want to keep the swap simple go with the 91 360 it has good heads on it already they should be 308 castings a lot of super stock racers used those in the past yes highly modified just like the other heads in super stock but there is a reason they used the 308 castings over the older castings they made more HP.
350HP from that 91 should be pretty easy to do with a camshaft regrind a RPM intake and headers.
Im not sure but seems like the accessory mounting bolt holes are a little different on the Magnum and LA heads so im not sure if all your LA brackets for the alternator and P/S and A/C are going to work with Magnum heads without modifications. I have a set of Indy/RHS X heads on a LA engine and they have the Magnum accessory holes on the ends of the heads and I had to modify my LA brackets to work with them not a huge deal but I had to modify one bracket cut it and make it shorter and weld back together and make another bracket from scratch.
Also not sure how well LA headers that you will be running in your Scamp match up with the magnum exhaust port most say they do though.
For 350HP the LA is the easy swap. I don't see the Magnum being that much better than a 91 360 myself yes it has a half point more compression (run thin head gaskets to make up the difference) either engine will need the cam reground or changed, both need a RPM intake and headers. Heads are not that much better on a Magnum compared to a 308 head casting 360. Main advantage a Magnum has is 10 bolt valve covers get a good set of cast Mopar Performance covers with a set of Super Performance gaskets.
Yes the Magnum has a few advantages stock vs stock but when you start hot rodding and he has 308 casting heads already on the 91 I would use the 91 the Magnum heads all seem to crack also even though it doesn't seem to cause any problems in most cases.

Advertised compression may be 1/2 point but in reality actually measured it is more like 1 point difference. The 91 TBI engine came with thin sheetmetal head gaskets, unless you get a custom cometic or copper gasket you are going to have to put something thicker than stock on it. The magnum is easy to put a thinner one on for even more compression. Way too many people are scared of a little extra compression, why not max it out for your fuel? What other mod can you do to get better power every where in the power curve and get better MPG for as little cost? Combine it with some good tight quench and the difference it makes is very impressive.

For what it's worth I have had equally hard time if not harder time finding uncracked 308 heads. Just less of them out there.