Funny, that was my first thought (convert to BW) as probably much easier to source. However, I wasn't sure what else was involved as I did read that they changed the diff ratio on the MK111 autos but whether that was just to bring it in line with other P5s I don't know and they fitted a separate transmission oil cooler.
I did think of changing gear boxes but there is a lot work involved i hope to source a crankshaft at the worst way I could use my one but i would sooner do a straight engine swap instead of taking my one apart
If you have a really good (MK3) engine I truly wouldn't be mucking about swapping the crankshaft with something of unknown condition/serviceability to fit a DG automatic unless you want to thoroughly rebuild the bottom end of the engine. It will definitely lead to tears. Truly it's much easier to fit a BW35 (upgraded) to the latest specifications or at least P5B equivalent to the engine.
As for the diff ratio, the 3.5 in the MK3 really is too tall for the weight of the car making them very sluggish to drive. A 3.7 or most likely what you have (3.9?) on the car is more suitable. It would also be definitely more responsive and lively to drive especially if you have Harvey or someone of similarly knowledgeable setup a more current valve body in the BW35. This will provide the car with part throttle downshifts at light throttle settings.
There's also no shortage of BW35/40 transmissions, rebuild kits and parts. They're also easier/cheaper to rebuild than a DG trans. Using a floor mounted selector is easiest/most straight forward but you can adapt it to a column selector if you really have the desire and patience. You'll also need to fabricate or adapt a rear trans mount and a suitable linkage for the transmission kick down cable.
There's more than enough expertise on this forum to guide you through the process.
If the crank fits a BW35, then I believe it will be a MkIIc or MkIII motor. In which case the crank journals may well be different. I know for a fact that the rear main seal dia is different between MkIIb and NkIIc. I expect Phil will confirm re the journals too.
The problem I have is I have a mk11 3litre auto with a Dg auto box I’ve got a rebuilt 3 litre engine from a mk111 the crankshaft will match a Borg Warner 35 and a manual gear box but not a Dg auto box so if could get a late mk11 crankshaft I would fit to my rebuilt engine but the crankshaft I need must be from a late mk11 thanks for input on this issue
Hi thanks again for your help my car is a mk11 1966 coupe chassis ending C engine number ending in C l have a rover parts book it my be wrong but it shows crankshaft suffex C and mk111 the same size journals my engine tired but useable I was hoping to get a crankshaft from a late mk11 auto which would take a re grind to fit in my re built mk3 engine at the worst way I could use my original but that means the car would be off the road a lot longer hope that makes sense
Gerry unless the conrods, piston weights and crankshaft weights are all the same engine to engine, fitting an odd ball crankshaft will affect the engines dynamic balance factor. The 6 cyl engines are supposedly finely balanced. If you manage to fit the non-original crankshaft to the engine the fine balance associated with the 3 litre may be lost. There's never a cheap & easy solution to doing what you want to do.
Do you know what has been done to the "rebuilt" engine?
Rather than selling it, you might be better off stripping it and re-using some of the expensive parts like pistons, cam-bearings (especially cam bearings), oil pump. Worth inspecting the heads on both to see which has been skimmed the least, which inlet manifold has the least corrosion, and so on.
Of course, if "rebuilt" just means re-bore and new big ends, then your plan to sell is good.
You sound like you already know that a well done complete rebuild of a 3-litre is not trivial either financially or in time taken.