Porting the current MP heads is a better choice performance per dollar. Send them to MCH and have them CNC'd.
That much guide clearance definitely isn't a good thing, but it wasn't causing much, if any, of your oil consumption. Especially considering it was the exhausts and not the intakes that were worn.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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