The 308 is the best OE iron open chambered SB head & the mag is even better. As you know you need the mag valvetrain related pieces for the conversion & a mag intake or redrill the head intake holes & some have even redrilled the LA intake for vertical holes & used a long bolt with a bushing sliced at an angle on one end. You may need adjustable pushrods and the P5007477 MP pushrods for the conversion may work but I think they are NS1 and they are pretty close in length to the adj MP ones I have. I just posted the measured lengths of all of them the other day for a guy on here but I think I tossed the scrap of paper. Good info on the large pushrod holes so you only have to pop a valve cover to verify. As said reportedly alot of em (OE used mags) have cracks but also reportedly the cracks ain't a dealbreaker & the heads are still useable so the cracks (if present) must not be in a vulnerable area. As you know the mags are closed chambered so the CR will be alot better than using open chambered heads which is another perk. EDIT the better combustion chamber will likely let you lower the total from the SB tried & true 35 down to 31-32 degrees. Check the deck surfaces for flat & good idea on the intake surfaces also. Holler how it works out when you are finished