I made a jig,essentially, that registered on the dowel pin holes in the bellhousing and the pump housing register on the trans. It held it all in alignment during welding. The proof of that is in the fact that the runout was very minimal after it was all done. Also after welding I put the whole case in the lathe and trued up the face so it is perpendicular to the C/L of the crankshaft and parallel with the engine block mounting face.

I actually made two - the first one had some slight problems I chalked up to learning. It would still work, though.

Two things that are interesting:

1) There is a certain point on a 727 case where small and big block cases 'come together' - that's where you make the cut. The match up is almost perfect at that point.

2) When welding the two pieces together, a lot of amperage is needed due to the large heat sink effect of the aluminum. .080" disappeared in the process. What that means is I had to leave .080" extra on the bellhousing (or on the case) and it would 'suck in' during weld to arrive at the desired final case depth (the distance from the face of the bellhousing to the face of the pump register).

One other thing - the aluminum of the 727 case, being over 20 tears old, had a lot of oil soaked in it. No matter how much it was cleaned ahead of time, it would 'boil out' and made welding tough.