Good way to waste my money

[xbacax]

Go dual springs. Even a mild Engle 110 with the heavier 40x35.5 valves should use dual springs.

 and if I'd stay with 35,5 x 32 ??

[Zach Gomulka]

35.5x32 is ok with single springs, but it also depends on cam. There are many variables (and opinions), but if you stay under .450" valve lift and no more than 6k rpm good single springs can be used. For example an Engle 110 (.430" with stock 1.1:1 rockers) will pull to about 6200-6300 max if all other parts are up to the task. You do not want valve float from too little spring. You also do not want excessive spring pressure  that is hard on parts and raises oil temp.

Your carbs, exhaust size, and 1915cc displacement are better suited to the 40x35.5 heads. It will also allow a more aggressive cam to be fitted.

[brian e]

What about ported stock valve heads, dual springs, an FK42 and 1.25 rockers??

Similar .050" lift to a 110, but a little quicker ramp, and a little more lift. 

[Jim Ratto]

What about ported stock valve heads, dual springs, an FK42 and 1.25 rockers??

Similar .050" lift to a 110, but a little quicker ramp, and a little more lift. 

35.5mm intake valve is going to "peak out" at about 4800 rpm in 1915cc, and will run out of breath around 5300. For a Bus that would be alright, but for a hot street car it would be yawn city.
Using such a small valve in a displacement like this will actually NARROW your powerband. You're choking the cylinder off.

The 1915 (for street) works best with W120 or W125, depending on heads and where you want it to run. If you wanted to go super hot, the K8 with 1.4/1.5 and 48IDA Webers makes for a scary ride. The FK10 in 1915 is probably bordering on going too far. I helped with a 1915 with K10 and a set of high CR midget heads with 44 x 37 valves and it didn't get out of bed until 4500. Another 1915 we used same heads but an FK87 and it ran from 5500 to 9000. Not a good idea for a street car.

My vote is for Engle 120 or 125 or Web 110 or Web 109 with 1.1:1 rockers and 40mm valve