That TRW is much stronger than the original springs @ 373 lbs. (vs. 307 and 318) per inch deflection.
Competition Cams #910 is even stronger at 415 lbs./inch:
OD 1.354", ID .940", assembled @ 1.45" gives 92 lbs. closed, 279 lbs. open to .450" lift
There is a wide range of 1-1/4" OD dual springs (doesn't fit the head directly but requires a spring cup) including Crane 99848, Crower 68301-3, Crower 68301-1, Comp. Cams 981.
The highest safe pressure on a flat tappet cam is fairly modest, anything above 280 lbs. is at risk.
Any roller is billet and able to withstand much higher pressure but, as said, needs much higher spring pressure (the tappets are heavy and the action violent). Bigger springs are available but may need the seating area on the head machined, guide cut down, etc. but the rest of the valve gear (rockers, stands) aren't that strong.
Are you sure a roller is necessary?
