He sure liked his chrome ! That is a very desirable T model Hi power from the 60s-early 70s. if you take the grips off if they are original they should be red inside . They did make nickel plated HPs it would need close inspection to tell if it is factory. If in good shape mechanically and factory Nickel you are looking at $2000 value. If it is not factory but works well then up to $1000 for the right person or $700+ or so on Gun broker. Both guns are in high demand but the Hi Power more so.
BTW , although not telling you to do it, many folks have shot many rounds of the lower powered .45 acp loads thru Webley Mark VI like that with no problems if conversion nicely done. The .45 Auto Rim should fit if properly shaved and is loaded to lower pressures pretty close to the final military Webley loads
https://www.outdoorlimited.com/hand...c45ar230-230-grain-lead-round-nose-50-rounds/
. Id keep both guns if they were my dad's . Use Ball ammo (FMJ) in the Browning as the early T models don't usually feed HP or SP that well. Be sure to buy the Mecgar mags which are quite reasonable and work best in those guns
https://www.midwayusa.com/product/1371114282