Ford never installed the 3valve in the econoline, the plug issue is from people that change plugs and are scared to really torque em down, about 25ft lbs in good, if they dont get tightened down and then they start working loose and them it pulls the threads out, They dont just blow out.
2004 Ford E250 5.4 4r75w dana 60 with 3.73;'s (Current)
1992 Dodge B350 360/46rh non lockup /9.25 rear with 3.90 cogs (sold)
1986 GMC Vandura 2500 305/TH350/3.08 rear (Sold)
1994 G20 Ex Virginia DOT crew van 305/4l60/3.42 G80 10 bolt (Sold)
1969 Chevy G20 Sport van 230,3 on the tree, 12 bolt with 4.11 cogs.(Sold)
2004 Chevy Express 2500 4.8,4l80E,3.73 (sold)
1990 ford e250 club wagon 460.E4OD,dana 60 rear 4.11's (sold)