What sort of .22 conversion were you contemplating? I note Numrich has M2 bolt handles and bolt heads.
A wide variety of centerfire service rifles have been set up in .22 for training purposes. Some were conversions, others purpose built rimfires.
Offhand, I can think of the Martinis, Lee Enfields, Israeli K98K Mausers, P'14 and M1917, Swedish 63s, US Springfields.
An important consideration is making the barrel breech face available for insertion of the diminutive .22 cartridge. The Martinis and Lee Enfields are easy from this standpoint. The Israeli conversions are painful. The rifles which use a two piece bolt with a dedicated rimfire front end may be the slickest. These would include the Springfield M1 and M2, the FN made Israelis, the Belgian P'14/M1917s, the Lee Enfield No. 8. I've done No. 4/No. 7 and SMLE .22s. Have been thinking about trying others. A Mosin Nagant would be fun.