The easiest thing to do is to replace the veneer adjustment plates with turnbuckles. You will also want to replace the forestay turnbuckles with a Johnson lever. Even with the Johnson lever released you will still have to force the mast using a halyard attached to an anchor cleat. If you attach it without slack you can lean your knee into it to apply enough tension to put the clevis pin in.
Doing his will save you a lot of time.