Here's a comparison of the two timing side castings with the potential replacement on the left and the original on the right. Both have the same (basic) casting number and are marked OHV. The main appealing features of the potential replacement are:
1) The casting is intact, has good lugs and as far as I can see so far no cracks
2) The bores of the cam followers are not parallel and the follower guides are as intended (thin-wall bronze(?) tubes for full diameter followers)
3) Good, flat, non-scratched oil pump mating face
The main drawbacks of the replacement are as previously mentioned, the throat is slightly over size and the the head bolt holes are in the wrong positions.
One other discrepancy I have spotted is the timing wheel shafts each have two (bi-directional) helical oil grooves where as the originals have only one (unidirectional) helical oil groove. Am I correct in thinking the bi-directional grooves would provide better oil distribution along the length of the shaft whereas a single groove will tend to force the oil to one end? Is this likely to be a problem or an improvement?
The main drawbacks with the original casting are:
1) Possibly holed case, re-instated with very poor replacement lugs.
2) Numerous cracks between, for example, the main bearing oil way and the side of the casting
3) Very poor oil pump mating face (would need re-machining flat and possible need for a spacer plate to replace the missing material)
4) The register to prevent the main bearing rotating is missing and hence may well be the primary cause of the lack of oil/multiple seizures
5) Great chunks of the casting missing (for example see around the inlet cam follower)
6) Worn, non-standard cam follower guides and followers still stuck in casting - maybe the act of "forcing them in" caused a lump of the casting to break off?
Anyway, the replacement generally looks to be a lot better bet (at least to me at this point) providing the throat diameter can be reduced and, most importantly, the head bolt holes can be re-located in a manner that will be adequately strong enough to withstand the loads created in this most critical area. Time will tell ...
Alan