The old P&G valve gapper was bought out by Edelbrock. Same exact gapper as the "old ones" except they cost over $50 now. When I bought mine in 1962 it cost $9.95. I still have the original box and instruction sheet.

Ran a Delorto 48mm set on my 427 BBC (sorry for the GM reference but cubes are cubes) many years ago and agree with the comments. Had run a 750 Holley and the Corvette 3x2 set up previously on the engine and the Weber styles gave a huge improvement in low and mid range torque but ran out of usefulness at 6000 RPM's. 58mm would have solved this problem but were hard to find back then. Any more cubes than 427 would make the 48's even more limited in RPM's

If you are willing to go with a solid lifter cam with big numbers of duration and lift you will need huge amounts of valve spring pressure. This is tough on rocker system and will only make it not street friendly by hurting low and mid range HP and Torque. Depends on what you want to do with it when done.

Have a stroked 428 built by a professional. It has a 4 1/4" stroker, 0.010 overbore for a total around 462 cubic inches. Mildly ported quality aftermarket aluminum heads and a somewhat mild roller hydraulic cam (232/240 @0.050 with .585/.615 lift)  and 10.2 to one compression ratio. Induction is  FAST EZ-EFI 1000 CFM throttle body and 8, 38 LBS injectors. Dynoed out of the box, with no tuning or break in, at 534 HP at 5900 RPM and 560 Lb/Ft.
I wish we had 98 octane in states. I would be running 11 or 11 1/2 compression and a slightly bigger cam without fear of problems. Seen many FE with this combo at around 600 or more HP. Good luck and have fun.
BTW, what is the per gallon or liter cost of the 98 in Norway?