1968 C10 6 cyl to V-8 conversion

[aprilg57]

I have a 1968 C10 that I am converting to V-8. The bell housing, flywheel, pressure plate, clutch & starter all work with the V-8. The problem I have is that the clutch linkage interfers with the exhaust on the drivers side. I'm using a 68 Impala exhaust manifold to be able to use the alternator mount. The angle to the rear appears to be the same as on my 1968 GMC 3/4 ton with a 327. The difference appears to be that the GMC engine is mounted a little further forward than the C10. There are 3 holes in the frame for the engine tower. The GMC uses the front 2. The C10 uses the rear two.
Question 1: Under what configurations were the front 2 holes used? i.e. my GMC has the 4 speed. Is that the reason or is it the fact that it's a 3/4 ton or ?
Is there another manifold that dumps straight down but still has the alternator mount bolt holes on the end that I could use?
April