sharing and offsetting pensions

My husband and I both have final salary pension schemes, investments held within an ISA and other investments / savings held outside an ISA. My husband also has a SIPP. We are both in our 50s and drawing income from our final salary pensions.
We have agreed to share everything 50:50. As far as our final salary pensions are concerned his is approx £28,0000 a year and mine is approx £14000, so we have agreed that I will get £7,000 a year from his pension to even things.
We are going to have to engage an actuary to calculate the % of his pension CETV to be transferred to achieve this
He also his a SIPP which he isn't drawing yet, so although it is a pension he says it can be treated as a pot of money in the same way as our ISA investments although the tax implications are different.
He has approx 300K in his SIPP and 300K in ISA and 50K outside an ISA, I have approx 400K in an ISA and 50K outside an ISA, which means that to share 50:50 he would need to transfer 100K to me, but is this fair as the ISA is tax free and only 25% of his SIPP is. What is the fairest way to share these assets, how do we value his SIPP taking into account the tax implications or do we need to engage an actuary to work this out ?

If you take money out of the SIPP then 25% will be tax free and the remainder will be added to your taxable income for the year. Withdrawing £100k to give to you, depending on whatever other income there is beside the £28k, could make for a large tax bill.

If he were to draw down the SIPP over a number of tax years to ensure that he never paid more than 20% tax on it then in theory it is currently worth £75k tax free and £225k taxable which would be tax bill of £45k.

Perhaps you could agree that it has a notional value of £255k for division purposes?