[1QuickS]

The "0R" manifolds were for 911S and had 35mm exit diameters, the "1R" were for the other engines and had 32mm exit diameters. Your manifolds were taper bored to a somewhat larger exit diameter.

Magnesium welding & machining will cost approximately the same as buying new PMO manifolds.

A summary of intake manifolds:

I have reviewed a selection of OEM intake manifolds to help answer some questions regarding individual variations between the years from early 1966 through 1970. I reviewed samples of these manifolds for each production year so I feel confident the gamut of variations is pretty well covered. Each of the manifolds has a date of production cast into the body except for the sand cast version. Surely there are manifolds with 1967 date codes and conical outer runners to coincide with the design change. I assume the oblong outer runner cross section was an attempt to accelerate air flow to help make up for the longer runner length. Also, early 1967 cast manifolds did not have the “Sportomatic”ports of those cast later in the year for the 1968 year model. This type of change within the year of casting is to be assumed in general regarding design changes over the years.

Info presented in no particular order:
• All manifolds are magnesium; earliest is sand cast and all others are die cast and have date codes
• sand cast, w/o mfg date; manifold part number: 901.108.321.01 with oblong outer runners; 34mm
• die cast, 1966, 911S manifold has part number: 901.108.321.0R with oblong outer runners; 35mm
• die cast, 1967, 911S manifold has part number: 901.108.321.0R with oblong outer runners; 35mm
• die cast, 1967, 911S manifold has part number: 901.108.321.0R with conical outer runners; 35mm
• die cast, 1968, 911S manifold has part number: 901.108.321.0R with conical outer runners; 35mm
• die cast, 1970, 911S manifold has part number: 901.108.321.0R with conical outer runners; 35mm
• die cast, 1966, 911N manifold has part number: 901.108.321.1R with oblong outer runners; 34mm
• die cast, 1967, 911N manifold has part number: 901.108.321.1R with oblong outer runners; 32mm
• die cast, 1968, 911N manifold has part number: 901.108.321.1R with conical outer runners; 32mm
• die cast, 1969, 911N manifold has part number: 901.108.321.1R with conical outer runners; 32mm
• die cast, 1970, 911N manifold has part number: 901.108.321.1R with conical outer runners; 31.5mm
• starting in 1967, reinforcing ribs extend from the bottom flange up the exterior of the runners; 1968 and later manifolds have larger and longer reinforcing ribs
• starting in 1968 the lug for the 8mm shaft for the bell crank has an added reinforcing web
• 1967 and later have ports for Sportomatic and/or other vacuum accessories; early castings in 1967 did not have these ports
• The sand cast manifold was for the first few 911s supplied with Webers which began to appear in Feb 1966 with engine #907001 as the Solex carbs were phased out.
• The early sand cast manifolds and those die cast in 1966 were finished the same as the early Solex manifolds with silver/gold magnesium chromate
• By the time the 911S appeared in July66 the sand cast manifolds were most likely replaced with the die-cast manifolds of two designations having either the .1R suffix for the Normal 911 or the .0R suffix for the 911S