I am undertaking a engine swap in a 68 deluxe, she's getting a 1310.

What pulley should I use, I have the choice of either single "v" & double "v" versions, because of the thicknes of the face of the double "v" it appears that the pulley sits further away from the water pump & the fan blade closer to the radiator buy about 5mm or so, using the single "v" the fan blades are very close (3mm) to the bottom pulley.

the single "v" was from the old 998 & the double "v" from the new motor, I assumed the double "v" was from a late model running A/C etc.

What pulley should I use?

currently running a 16 blade metal fan

The double V pulley was from the air pump equipped 998s etc of 1977-78.
I prefer the tin single V one...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

if I use the single v, do I need to use a spacer, ie will there be any misalignment between the alternator & bottom end pully?

You should NOT need a spacer behind the fan pulley.
Mine has one in there, but only because I use a belt drive cam kit (not a chain) and this pushes the bottom pulley out slightly.
Put a straightedge there to check alignment if in doubt.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Use the twin pulley and run dual alts That would be AWESOME

From my experience the Water Pumps are not alway assembled accurately and the drive flange face is not always in the correct location, so some variation can be attributed to that. I'd suggest a standard single V pulley and add the thin (~4 mm) as required. Just check clearance from the engine pulley / harmonic Balancer and of course the radiator.

Don't be tempted to bend the fan blades.

got it sorted, using the single v.

As GT Mowog suggested the pump drive flanged was a little too close to the pump body, pulled it out a few mm and all is good.

cheers & thanks for the advice

On ya junior