SP1 currently has original 35mm forks which are tired
Been offered a T5 front end with 38mm forks.
Is the headstock the same on T5 as SP1?
Will they just “bolt on”??
T5 is probably around the time they changed from short headstock to long so that might be an issue. Not sure where you would find out which have long and which have short. Do you have a copy of Guzziology? That should tell you.
sadly don’t have guzziology.
Looking on the Stein Dinse site looks like the T5 has the longer headstock.
The front end is miles away hence my asking as I can’t measure myself…
From a quick browse it looks like the T5 is right on the time of the changeover. If it is an early T5, you might be OK. If a later series 2 or 3 then it has the longer headstock.
"Compared to the T5 series I, the T5 series II & III have a longer steering head with a gusset to the frame backbone."
Another thing to be aware of is that some T5’s had 16 inch front wheels, so presumably the forks may be longer.
Edit One possible way to make it work would be to press the stem out of your SP bottom yoke and to fit that into the bottom yoke from the T5. Assuming the fork lengths are the same or close enough that you could drop them through the yokes a bit.
so the stem is normal ie not the longer one
But the sliders are for 16" front wheel so the answer is yes the yokes will fit the headstock but the forks won’t work 
I wouldn’t like to say if it will work or not. Depending on how technically minded you are, it probably could be made to fit. You would really need to see it alongside your own forks to say for sure.
Your original stem could probably be fitted to the T5 bottom yoke if necessary. Then you need to look at the length of the forks.
Had them up against my forks, that’s how I know for sure!
If they are just a bit longer, could you drop the stanchions through the yokes by an inch or so? Or can you get different stanchions to fit the lower sliders?
Alternatively, see what other options are available to fit the yokes, ie other bikes with 38mm stanchions. A google search for Guzzi 38mm Forks comes up with a few possibilities such as this.
https://www.gutsibits.co.uk/pr/TheShop/index.php?f=d&Model=&q=SUA00375
I’m going to make do with originals.
The reason for asking is that they were free and in better condition than mine and 38mm instead of the spindly 35s
The brake mounts are different to accommodate a 16" front wheel.
Could make brake mounting brackets I suppose or even get smaller discs but then it all gets a bit complicated.
I have since discovered that T5s had the normal headstock and the longer headstock and either 18 or 16 inch front wheels.
Evidently the T5 struggled with its identity!
I think the Le Mans Vs also came with 16 and 18 inch front wheels but always the longer headstock…