748 SP has steel rods but the race type (basically lots stronger than standard and about the same weight)

748SPS has Ti rods but not the race style, so lighter than standard and a little stronger (tho not as tough as the SP ones) a homologation thing really.

Corse rods are lighter and stronger than both but are outrageously expensive!

So, if your replacing rods with used ones i prefer the SP steel ones as they are bulletproof. also, the ti bolts on the ti rods can only be tightened 3 times and should be checked for stretch. (they are about £100 each! Ouch)

On the 748 the valves are the same size from BP to SP to SPS as are the heads (apart from cam profiles) But the pistons are high compression on the sp/sps not bp which is what makes them feel sharper than bp's. so if you're buying second had pistons be carefull you dont put the flat top BP ones in there or you'll have a low compression motor with SP cams and it wont be very happy.

if its apart, and you are buying pistons and barrels, get the 853 cc kit. its mega! but thats a different story!

when you have your pistons, rings, rods and crank on the bench, send them off to be balanced. daft not too when its apart, should cost about £100 all in and will make a big difference.

Good luck.

Is the compression ratio of a SP altered that much when fitted with BP pistons, I only have the Haynes manual for the 748 and it quotes 11.6 to 1 for the SP and 11.5 to 1 for the BP.
If the heads and valves are the same I wouldn't have thought dropping 0.1 on the compression ratio would make much difference.

Simon I should be able to get them over to Dave's no later than Wenesday afternoon although it may be as early as tomorrow if work doesn't phone needing my services and your still happy going with BP ones.
As I said I also have a few other internals so was there anything else required in the bottom end.

Dave's not been in today but I'll check with him what is needed and call / mail you tomorrow. I don't want to mess you about and make any unwanted trips so I'll confirm asap but depending on finances, it seems that we may go the 853 route anyway. Unfortunately, I don't have enough tech knowledge to know whether your parts will fit but again I'll try to confirm with Dave tomorrow.

Laters

simon