I would caution against just hauling it up to the improvised A frame - as there is no transverse control with this.
BUT if you lift the mast via the spreader hounds without base fitted to pivot, then you may be able to complete without stressing the base mount. The A frame being immediately above base pivot point will then allow you to fit the pin / bolt and secure. Assuming pole and boom are long enough !
Usual A frame method is to have A frame rise with mast closely coupled so as to stop mast falling of to side etc. and stressing the pivot base. It is even more important if you have the blade type base fitting and not the substantial tabernacle type. But to do this A frame basically has to be at same pivot level as mast base if mast is pivoting, not necessary if mast spreader height is less than boom / pole height of A frame.
I have to lower / raise me mast a number of times each season to get under town bridge. I've tried allsorts - even spinny pole as extension to front of mast (very nearly bent mast that time !!). Final solution was to make sure I have 4 good guys stationed appropriately with stays / mast in "hand" and stout line from windlass made of to forestay to control lowering.
Compass24 have a mast "derrick" system which is not cheap but solves this problem.