RL 19, IMR4350 and INR 4831 should get you where you want to be with the 145 gr Speer.
57.0 grs RL 19 and a 140 gr BT or PT went sub MOA in 3 different 280 Rem rifles.
I worked with 145 grain Speer Grand Slam at one point in the past. The load gave me decent velocities and reasonable accuracy. I was using WMR, which is no longer manufactured. I have a good supply, however, should I ever wish to retest these bullets.
I've loaded the 145 GS with excellent results over IMR 4350. Not going to post my loads as they are on the warm side of published data (mauser 98 action) but they parallel Lyman data. I would start with 4350 as it has worked well for me and is relatively available currently.
I worked up a load for the 145BT in my .280 awhile back...Nosler brass/BR2 primer/ IMR 4350 55gr. 2950 from a 22" barrel, moderate pressures in my rifle. Good luck to you. Oh yeah, I also used 59gr R22 with the Nosler 150 ABLR with great results. Good luck to you Pard!