I have a 318 magnum block and was considering a stroker kit to a 390. I want to continue running the fuel injection and magnum heads. My concerns are...Do I need a different flexplate? Are 360 heads better? Will a M1 intake support this with a larger thottle body? My intention is to get a 99 durango into the 13's. Thanx

I do not believe you need a different flex plate. Magnum heads are all the same, they came on both. If you need heads the I would call Hughes and get a set from them. For a bit more cash it would be worth it. I would think an M1 could handle it but Hughes also has an RPM intake kit that might work better. If you haven't already then think about injectors, chip flash, computer, exhaust and what ignition will work. I am not affiliated with Hughes and I am not an expert. I plan on doing the same with my Ram so I am just pointing out with what I have read.

5.2 magnum are internally balanced?

just have your new 390 internally balanced...then you can use your current flexplate...

Thanx ya'll. I was more concerned with timing on the flexplate moreso than balance. This doesn't sound like a common build so I think it'll be fun. I have an email in to hughes for specifics but I thought I'd ask around.

I've seen a few 318-to-390 threads on here, do some digging and you might find some more info. You'll have to filter out the 'get a 360 to stroke instead' stuff though.

I think you'll have problems getting the stock efi system to work with your new combo. You would need bigger injectors and a computer recalibration. The injectors are easily doable, however I don't know if anyone custom retunes the efi computers for those things.